I never tried it. My only contact with the fediverse was through Lemmy.
When I became aware of lemmy it was first through the piracy subreddit doing the exodus and the head mod db0 mentioning the new piracy community. I wasnt aware of instances at the time and signed up on lemmy.ml because that was the first thing that popped up.
Later I realized I didnt want to be a part of ml and switched to my current instance.

Same goes for matrix. Signed up on element and now I dunno if I wanna stay there or leave. No special reason to do either.

Last time I heard about Mastodon it also doesnt inform about instances.
First google on mastodon leads me to mastodon.social.
A few links later (Info about an animal called mastodon, mastodon.social, google news widget, google info page widget and a "people also ask" section) I get to the joinmastodon.org page and first leads me to mastodon.social and a server selector.
My grandmother would be overwhelmed, my mother would ask me if the site is safe (I warned her to be wary about domains switching) and I assume other more tech iliterate would be just joining mastodon.social totally defeating the use case of deferedation.