There are assets in the game that are, mostly subjectively, just too close to Pokemon models that there has been internet flamewars around that topic.
1. https://m.media-amazon.com/images/M/MV5BNGJhOGJmZGItNjQwZS00...
I think the game's massive instant success is a circumstantial evidence in its own, it's just inconceivable a lookalike indie game on Steam becomes a ~20th top selling AND second most simultaneously played game on PC ever. Granted, games like Stardew Valley and Half-Life 2 sold more over longer time periods, but never even reached the same peak player counts.
The game is insanely popular right now, which is reason #1 its getting so much scrutiny.
The similarity is more blatant than any Pokemon-likes I've seen. By a large margin. It also has other meme worthy aspects (like the Pal-labor gun manufacturing thing) that Nintendo would absolutely not want to associate with the Pokemon brand.
Personally I think the game is great. I'm having a lot of fun playing it with my friends. I hope it continues being popular and that the developers get to realize it's full potential.
I don't really give a crap what Nintendo thinks about it, I don't see them offering anything similar.
2. It kiiiiinda sorta vaguely looks like Pokemon
3. Everyone and their dog is all "haha nintendo won't sue.. they won't sue, right...? right...?"
[0] Not an afternoon project, but also very much not out of Nintendo's wheelhouse.
Actually, the anime even says outright that one of the Pokemon is basically extinct because it's so delicious: https://www.youtube.com/watch?v=Wrd128i8YGI
Nintendo will accept they need to have an answer to "So are all Pokemon vegan?", but will neither advertise it, nor push people to question what all the people and pokemon eat.
They have very different markets, and strive to project different images.
They effectively are trying to kill the community-run Smash tournaments through legal.
There is no better perfect fit for an MMO than the Pokemon world.
