It’s because Niantic have actively made the game far worse in the past year, after a few quite decent years through the pandemic. Them using ai to generate the latest artwork just epitomises how ridiculously lazy they’ve gotten. The artwork on the loading screens was one of the few examples of legitimately good work they ever produce, so now they don’t even have that.
I don’t think anyone actually cares that it’s ai, but it is classic Niantic to just slap together ai artwork and make no attempt to hide it.