IIRC Showdown has a tacit agreement with TPC (or at least has historically; unclear if Champions will change anything in the future) and is allowed to exist so long as it follows certain rules. I can't find it right now, but I swear I read a comment from Zarel, the creator of Showdown, explaining what some of those rules entail, including an agreement not to include any moves or mons that haven't been officially released in the mainline games yet.

Other people have speculated that TPC can't/won't axe Showdown because they know that VGC players rely on it heavily to test out team comps before official tournaments, and Champions doesn't seem like it fills the same niche, unless TPC is suddenly about to change their stance on genning :P

I think they killed it because they were planning on showing off their own remake

I think there are 3 rules to avoid getting the ninjas sent after you:

1) Don't try and make money 2) Don't do anything nintendo would realistically do 3) Don't touch mario. This one seems to be the most important. I see mario projects get killed all the time very early on in development, while am2r was allowed to exist until nintendo exercised rule number 2. I imagine the mother/earthbound fan works/translations will also be left alone if nintendo chooses to never touch that series again

Probably for the best seeing how many literal degenerates and sex pests there are in the scene, what with Nintendo being a family company and all.

edit: sorry downvoters, if you want to play with corporations you might want to remove the rapists from your ranks:

https://www.ssbwiki.com/2020_Super_Smash_Bros._sexual_miscon...