I think you should re-evaluate that assumption:
https://www.google.com/search?q=mastodon+instances+blocks+ga...
https://www.google.com/search?q=mastodon+blocklists
https://www.google.com/search?q=mastodon+blacklists
https://www.reddit.com/r/Mastodon/comments/kw8jht/how_do_i_s...
Also, expand the ">Moderated servers" heading and scroll down through the instances they black:
https://mastodon.social/about#unavailable-content
Why do different Mastodon instances decide on not federating some of the other instances?!? It's because the owners pay money for running their particular server which makes them feel entitled to run it the way they want.
The "pick any server, it doesn't make any difference, you'll see _all_ messages anyway" -- is not realistic given that each fediverse node administrator can exercise their freedom to choose what messages their server accepts.
That is true, but most Mastodon apps make multi-accounting a breeze, and I imagine the Lemmy ecosystem will provide the same functionality.
It also helps that Lemmy is trying to court the userbase of Reddit, who are already a pseudo-anonymous lot and in my experience don't seem to have as much of an attachment to their old content as Twitter users, deleting their old posts and accounts on a regular basis.
Originally, Google was pure discovery. There was no Google content, just links. That's pure discovery. A standalone blog is pure content. Together, you have a social system.
Separating those is a step to freedom from oppressive service providers.
It creates the possibility for a business model where subscribers pay for access to a big news spool and lots of groups. Just like USENet.
There will be some growing pains, but there will eventually be a continuum of "free" lemmy servers, for pay premium ones, and lemmy servers where the front end is only an app on your phone.
And they'll all see the same messages.