Slothtastic

or is it because Izkuthii were made by Flam and he didn’t wanna get rid of them?

it’s probably because they’re more than reasonably active and had a re-write in the works that was actually well done

Creatures/Magic are meant to fill specific niches and more, that normal Descendants are not able to with their ‘normalness’. I don’t see anything else on LotC that is remotely similar to Izkuthii, however, Satyrs and Cervitaurs are quite literally reskinned wood elves. Fae creatures should be mostly event creatures anyways.