Wait, this gets me to wonder - couldn't a Thief or a Rogue of Void technically just pull a genesis frog out of nowhere?

That’s the thing though- A Matriorb required a Rogue of Void to be inspired by a Muse of Space to be made. A Matriorb, as important as it is for Trolls, is just a biological thing coming from a weird alien bug. The Genesis Frog is the Universe itself. You can’t just materialize something like that without being extremely, severely overpowered, and it’d defeat the very purpose of SBURB if it were that easy.