TBH, i don't know entirely, it just "feels" like i want the instance i'm most interested in. Yes, local timeline is neat and a feature i'd like to be able to use, but the Social aspect of Mastodon (vs email) means i tend to view the domain as indicating primary interest. It feels like a badge of community/interest.

Not sure if it makes sense, just trying to explain what's going on in my head. As i have debated that exact question myself, internally.