Honestly, I'm shocked that mastodon.social *only* receives about 20% of new users. It's easy to forget that an even distribution of users is a very unstable equilibrium, and that there will always be factors that push users toward a small number of servers. Given this, the fact that almost 80% chose *not* to go with the 'default' choice is remarkable and demonstrates, I think, a lot of genuine curiosity on the part of new users about decentralisation. Not at all something to be concerned about.