The three things behind Pokemon being the superpower it is are: children, autistic manchildren and nostalgic normies.
Temtem has limited appeal to children. The designs aren't that cute, it has tranny shit that not only increases its age rating but makes some parents aware, and it's more difficult than Pokemon so kids can't just pick their favorite and stroll through. Plus, well, children don't have their own money most of the time; Pokemon has so much brand recognition that it is what parents will get their kids.
The autistic manchildren are too invested in Pokemon already. They talked shit about SwSh throughout all leak season, and guess what, still bought it. They have too big of a sunk cost to just leave Pokemon. They'd rather bomb Masuda's house to get him to change a thing in the game than actually look up a competitor.
And the normies - well, they have nostalgia for Pokemon, so they will pick up the nostalgiabait shit aimed at them like Go.
So Temtem aims at a very specific group of people - people who like Pokemon's general gameplay but aren't too attached to the IP itself, and who want this gameplay "improved"/"refined". And that is a very very small group of people. And trannies, too, which actually pushes tranny haters - that is, normal people - away.
