Basically, I have this story I'm trying to write in which there are an advanced space-faring species of precursors (very original, I know), which have been scattered throughout the cosmos as their original homeworld and most of their species was destroyed. They are almost all aware of the existence of other ones of them throughout the universe, but most are isolated from each other by vast swaths of space. They love to toy with the 'less advanced' species in the galaxy, too.
Their technology is millennia ahead of the rest of the galaxy, which makes them enigmatic to most other races. They are all biologically immortal and have incredible powers rooted in highly advanced scientific technobabble, which allow them to individually and personally manipulate space-time to teleport themselves and other objects, materialize matter and energy from higher dimensions, create highly sophisticated devices from nothing, fly and other such powers.
They are all incredibly intelligent and knowledgeable, have super-advanced senses and so on. Each one individually could take down a Starfleet, destroy a planet, or with great effort, rearrange an entire solar system. Effectively, they are on the level of Bill Cipher in his physical form in terms of powers. Akin them to the Q from Star Trek, even.
Now, this is just an example. In the actual story, I'll likely tone their powers down quite a bit if need be, but still. I have this idea that their species cannot reproduce or breed (they cannot have children), nor can they reproduce VIA cloning or just by creating a new one of them with their matter manipulation powers. Though I'm having trouble justifying why this might be the case.
It could simply be that they simply don't WANT to do so, that they have accepted the fact that they are the last of their kind, but I'm not a fan of that idea. Hence this post.
Does anyone have any potential plausible explanations as to why this race or ANY race this advanced in fact, DESPITE being so advanced cannot reproduce beyond the current generation?
Thanks in advance.