It's absurd the Gacha hasn't brought back ONE of them, especially in THE series for return appearances.
Really the Gacha as a whole feels underutilised, and I feel that's as much the reason it's not all that popular.
So many cool ideas could have came from it, it's giving insight to Pokemon used within the rest of the organization. Even Grookey, a Pokemon 'liberated' from it by the protagonists, a really cool concept to try for that matter, isn't really delved into that much in terms of trainer or how it was treated or even if it's mischevious streak stems from a criminal background. It came off like a simple case of Grookey not wanting to serve a bunch of squares, preferring the clueless kid who would let it get away with whatever it wanted.
It sticks out more since the whole show makes a point that Pokemon can NOT be sent to Team Rocket, it's the biggest defining moral difference between the protagonists and the TRio capturing wild Pokemon against their will. It's a HORRIBLE fate there. And yet all these Pokemon seem to be normal and content.