Don't have a publicly-viewable federated timeline. Bam, blocked.
BTW: Public instances of Hubzilla and (streams) never have such a thing. They could, they do have the technology, but the admins always decide against activating it in order not to be held liable for content that comes in from the rest of the Fediverse.
On Hubzilla, there is a way to make the public stream available and only show posts from that server. But most Hubzilla admins never turn it on and probably don't know it exists.
As an administrator, the only time you would want to turn on the public stream is if you are a public hub and accept new signups. It makes it easier for administrators and moderators to moderate the public content on their own server since they can see all public posts in one place. If someone is posting illegal content or spam, a moderator can see it, and remove it (and perhaps the user too).
But private instances don't need this since everyone on the server is trusted.
I was thinking about that the other day. Most fediverse servers won't even qualify to be federated with Threads. Especially single user instances, since they are unlikely to have a privacy policy for themselves and a public stream.
And they can only connect to Threads because Meta doesn't want to go after thousands of private single-user instances, clutter their blocklist with them and check every once in a while if they still exist to keep it from being clutterted too much.
Also, at least on Hubzilla and (streams), it's the single-user instances that are likely to have an actually public pubstream. But not necessarily the federated one that Threads wants.
There are concerns that your publicly posted information would scooped up by bots that scrap up public information on the web. Or more specifically, be used by Meta to build a profile on you, which it already does even if you don't federate with Threads.
People who are concerned about this usually choose not to federate with Threads, but they also would need to block bots and Meta specifically to fully be protected.
Others don't share their concerns as much, or are more selective about what they post publicly. Some platforms allow you to post privately, for example, and unless you are communicating with someone on Threads, Threads would never see it even if you were federated with Threads.
Also, having the biggest instance\service is a power because whatever you do you need to make sure it is compatible, so you end up servicing them first and foremost, and they can pull some strings from their side to change things for everyone.
I don’t have a FB or Insta account… for a good reason. I don’t want one. Apart from Meta existing solely to maximise shareholder profit (which sits weirdly with the fediverse) there is its user base to consider. Whilst undoubtedly there are a lot of them, how many would bring actual quality as opposed to quantity of posts? Also, the Zuckdroid. Need I say more?