That's just not practical for most people (the publishing part).
And in relation to microblogging, are you going to publish every 140-character, out-of-context thought on your personal website?
If you don't want to get your own domain and run a server (not practical for most people) you can still protect yourself from being stuck in a single silo by broadcasting to many social media sites.
Imagine if Bluesky decides to ban you, and continues to ban accounts you create elsewhere. Atproto ensures non-Bluesky PDS can see you, but you've lost 99% of the userbase.