Lemmy and other fediverses shows up on Google and other search engines

They really don't. The only way I get it is if I do something like "site:lemmy-instance ". It can be done, but I really don't think a lawyer is going to bother, much like they likely don't bother with smaller forums and whatnot.

it already happens

On lemmy? Can you give me an example?

they couldn't DMCA a parody anyways

They absolutely can. It doesn't need to be legal, just scary enough for the website to not bother looking into it further. That happens all the time on Github and Youtube, it's not exactly new.

Blocked

Okay. That seems a bit extreme, but whatever.