EDIT: I have been asked to create a more concise and specific question.
The question I would ask is what would be a (good) reason for my dragons as a species, having no inherent reason to share human values, to hoard gold?
Here are some background from TV Tropes to prepare for my question and discussion (see full page https://tvtropes.org/pmwiki/pmwiki.php/Main/DragonHoard for more insights):
In some settings, dragons tend to guard hoards of treasure — typically by lying on top of it. [...] Curiously, there is no consensus as to why dragons do this. Justifications in-story for why a dragon sits on a hoard, including backstories of how hoard and dragon came together, vary considerably. In some ways, hoard-guarding dragons are no different from other treasure guardians: [...] Dragons have a peculiarity, though, in that they are especially attached to gold: dragon-hoards almost always contain at least a substantial share of gold. Whatever the reasons, on average dragons show noticeably less interest in other treasures, like silver or even jewels. People have also long noticed — see that Beowulf quote — that dragons have no apparent use for treasure: they cannot spend, wear or process it. More often than not, they don't do anything beyond brood over or sleep on their treasure. Dragons, it was concluded, must be pathologically avaricious and stingy—kind of like a species of compulsive hoarders with a Money Fetish. In fact, up to the 17th century, dragons were considered the emblematic representation of Greed.
The idea to have dragons as a symbol of greed, seems to me to be a result of the human conceit that a separate species should possess the same values about gold and greed that humans do; a human conceit.
My worlds have dragons, very intelligent dragons I might add for context. I would like to evoke some typical dragon attributes from mythology, folklore and older fantasy, but I'd like to make justifications for them that would work alongside my own take on dragons. The question of the practical use for the dragons in my world to hoard gold has proven to be a challenge to satisfyingly answer for myself, in relation to the context of my dragons.
Here are some pointers of my worlds dragons that influence my thought on their gold hoarding:
As a species, they predate the existence of humans (homo sapiens), by maybe a greater time spans than mere millenia. A dragon species that predates humans shouldn't possess the same thoughts on and values regarding gold that humans do, but have their own reasons that existed before the human species and human civilization. They would have hoarded gold nuggets in the time before humans made coins and cups of the metal (and then some dragons would have gone over to plundering humans instead).
They developed the (supernatural?) ability to perceive the presence of (large?) concentrations of gold at a distance, a "gold sense". Before, I made this sound like a natural evolution, but my own idea was that the dragons, a species in possession of magic, modified themselves as a species to give them the ability. If they found gold important enough to modify their very species (think human gene-editing) to have an easier time of finding it, gold should have some practical use for the dragons.
The dragons are solitary creatures, each self-sufficient enough to survive and even thrive on their own without the help of another member of their species. Now, being intelligent, they could engage in some social exchange, there always comes the time for procreation, and some dragons might form pairs that last longer than they have to rear the young (who might be self-sufficient very quickly, being dragons). But I don't envision them conglomerating into settlments as a general rule (though a rare encounter with a village of dragons sounds interesting...); they could have a common culture, but perhaps nothing akin to a human society. The point of all of this being, the dragons probably wouldn't have use for anything, including gold, for monetary purposes (as in currency). (See also TV Tropes "dragon's cannot spend gold" for comparison.)
The dragons are intelligent and mighty in magic (I don't know how structured or wild their magic is, though), but they lack the limb appendages to make use of gold as humans do in goldsmithing and engineering. Some kind of magical technique could work as a replacement of human hands, I guess, but otherwise it's seems less likely that dragons would make use of gold as humans do. Also, as a self-sufficient organism mighty in magic, it would seem to me that the dragons would have had no reason to develop any such technology as humans might have done, so I would guess that dragon's would not hoard gold for gold's uses in engineering. I would rather think that there would be some reason rooted in magic. (See also TV Tropes "dragon's cannot process gold" for comparison).
Because of that last thought on a magical reason, I tried to research the magical uses of gold in real world mythology and folklore to use as a baseline. Here is a question I asked on the Mythology Stack Exchange for that purpose:
But I found very little that could be of practical use. At most, I found that gold is associated with eternity and immortality, and that Chinese alchemists might have thought that it could be used to confer immortality, or at the very least act as a healing agent. That last part sounded useful, but then I remembered that using gold for healing purposes is already in use in the Feruchemy of Brandon Sandersons Mistborn, and I don't know if it would be safe to use that idea (correct me if I am wrong here). (Regarding immortality, I find it of less use for my dragons because I already think of them as living forever barring mortal injury, though that could be changed to extremely long-lived, I guess).
Researching the reason for dragons to hoard gold elsewhere, I found some alternatives. One is the suggestion of dragons hoarding gold (or shining items in general) to attract mates. Another is that they hoard gold for just the reason to sleep on it, with gold being a soft metal (dragon's have armor-scales and probably dull tactile senses) that does not catch fire (from dragon fire-breath) and does not corrode (from acidic exudations).
They are valid suggestions, in that they give reasons that make sense, but I personally would like other reasons for my dragons. In context, if they went so far as to modifiy their own species to sense gold at a distance, it feels like it should be for a greater purpose than to find bedding material. And while finding mates definitly seems of greater importance than bedding material, I feel like it wouldn't justify going so far as to modify their species. As a side note I thought of as I wrote this, I would think that dragons would have it in their mentality that if their only reason for collecting gold was to attract mates, they would have refrained from introducing a gold sense into their species in order to make it a much harder exercise to find gold to attract mates, thus promoting the most successful dragons above the less succesful ones; a "winner takes all" mentality that seems like a natural fit for the very powerful dragon species.
Now, this question is asked in the name of world building for fantasy, so it doesn't need a science fiction answer, but a science fiction answer could also be usable in some fantasy.
This is outside of the question, but if the possible answers also could include other types of treasure that dragons could hoard (gems, silver, etc.), it would be a bonus.
The question formulated another way and as a reminder: A non-human (and perhaps non-scientific) reason for members of my dragon species to hoard gold, what would that be?
If anyone gives an answer here, I will make additions below this paragraph where I make comments that hopefully improve the discussion about this topic.