For example, mastodon and bluesky are different platforms. I have to have two separate identities. I don't care about either one of these entities. I'm just want to be me in both places.
I'm closest with mastodon right now. I have my own instance and I can publish what I want. People have to come looking for me and decide to follow. But bluesky people can't decide to follow me if they want to. The arbitrary boundaries of their platform prevent that.