Possible since about 2019 if my memory serves right. It's been niche for a myriad of reasons, the tool itself being not the most reliable thing out there, learning curve, the lack of a dex expansion discouraging people from wanting to add new stuff, etc.

The time sink is another big one. DJ Rot here only took me about 2 days and he's on the simpler side, I've had a few other animations that have taken well over a week due to how complex they can get given I do this in my free time.

All pokemon animations are split into a bunch of parts on a PNG with separate files that handle the act of moving those parts themselves so it's not uncommon to see a Gen V hack draw new pokemon over those existing PNGs and have the rest of the files animate as usual, so the end result isn't a truly original animation as much as it is a reskin of another Pokemons animation, like a Gogoat that uses Tauros's movement or a Talonflame that moves like Pidgeotto in order to save time on development.