It honestly makes a lot of sense to keep illegal content that's the source of frequent legal actions away from the largest general purpose communities. As you correctly point out it is extremely easy to join another instance where these discussions are allowed, and the larger instances have every reason to have a "better safe than sorry" approach to content moderation.
It seems to me the Threadiverse is too negative of the concept of defederation. It's a key concept of how the Fediverse works, and is supposed to work. The people on Lemmygrad is looking for a completely different experience from the folks over at Beehaw, so let them have it. Lemmy.world has become the largest instance, so naturally they need to have an approach to content moderation that is unlikely to land them in legal trouble. And even if they didn't, they'd be welcome to block discussions of piracy out of moral conviction or any other reason, just as their users are welcome to sign up somewhere else if they are looking for a different experience.
There was drama about defederation on Mastodon in the beginning as well, but I guess people coming from Twitter had an easier time intuitively understanding the appeal of it.