Seals are magical runes meant to restrain and restrict the movement of demons, limiting their range of movement and trapping them within the seal itself. Their are three variations of seals created for several classes of demons. Type 1 seals restrict the lowest classes, which are the weakest form of demons. Type 2 seals are for mid-level demons. Type 3 seals are made to restrict the highest and strongest class of demons. Applying the correct version of the rune is important to contain a certain level of demon, and knowing how strong the creature is beforehand is essential for the spell to work. Applying the most powerful version of the rune to a weak demon will not restrict it, and applying a type 1 seal to a powerful demon can be easily overpowered.
Seals are made through the use of mana, the magical energy that exists in all humans. Mages have gained mastery over their mana for the use of performing spells. To create a seal, a group of mages must work together and force their own mana into a created rune in order to power it. The more powerful the seal that is to be created, the more mana it requires from the mages to fuel it. Mana is a self-regenerating essence, so the amount that is applied will recycle itself and trap the demon within forever as long as it is not broken.
When items are created in society, there are usually several variations of it, with the cheapest being the most simple and limited. As technology grows and quality increases, it becomes more expensive compared to its predecessors. However, it can do everything that the previous generation could do much better and more efficiently, as well as add new capabilities that make it more valuable. The equivalent to this would be an Iphone 12 of 2020 to a blackberry of the early 2000s or a flip phone of today. A goal of magecraft is to create a seal that can contain all versions of demons regardless of class, in order to save time and expense, making it easy for mages to do their job without having to know the kind of demon they are dealing with beforehand, and no expense has been spared. However, all such attempts have failed.
What would prevent this kind of rune from being made possible?