Thing is, it's not in the mods or admins' best interest to leave it up in the name of "user choice" and "free speech", these platforms host the content on them and the people hosting it are liable for it, plus making people be able to opt-out of moderation actions would attract unwanted people to the community, the kind of people who would seek that violating content and interact only with that.

Lemmy is NOT a "free speech" or "user choice", nor are the majority of fediverse platforms. I think that's one of the biggest misconceptions when it comes to the fediverse, it's that people think it's that. Really Federation is ultimately the same as a centralized site, that is self hostable, but with the added benefit of these different self-hosted sites communicating and cross-posting to each other. While this would be considered decentralized at the end of the day the site owners are the ones calling the shots, the can delete anything they want, ban anyone they want, or sever connections to servers if they want. They are within their right because they own the site and pay hosting and/or maintain the servers. Why should they put themselves at risk for the sake of "user choice" or "free speech" when they don't owe you the user anything?

With Nostr it's different because operators can purge whatever data they want off a relay, but your account isn't bound to a relay and information doesn't need to be copied to every relay like with Fediverse's ActivityPub. It offers the "user choice" and "free speech" experience by cryptographically isolating the user from the relays and by using them as... well... relays instead of instances.

In short the reason they don't do it is because the way the Fediverse is built isn't really suited for it, due to both liability, and the function.

One could make a tool like Reveddit or Unddit for Lemmy though that fetches the removed comments from the modlog and puts them back in the thread, but that wouldn't be like bypassing or disabling moderation.