They had a few days tops to look and decide where they wanted to be. People didn't want to waste them on figuring out how/where they should join.
Hell, first time joiners don't know about the various dramas between popular instances either. You wanna know why so many choose .social? Because they don't have to figure out which server defederated which when they wanna talk with their friends. (Info they basically can't find reasonably without already being active here.)
Example, where do you post about anime on Lemmy? Choose the most searchable server, you'll find a dead sub with moderator drama. You have to be in the know to find ani.social.