mastodon.social will only get more centralized and is the only one that is benefitting from that change.
That basic hurdle is the reason why it is a barrier to many potential new users and it has traded complexity over ease of onboarding when trying to sign up new users (who are not techies or sys-admins).
One solution is to set a default instance. I.e 'mastodon.social' and tell users to sign up there. Again, that increases the issue of centralization. To prevent that, you close sign ups and tell users to sign up elsewhere. Then the issue continues on other instances.
Along side other issues, that is why new users just went to Bluesky or Threads instead.
Bluesky's AT Protocol was developed specifically to address what they saw as shortcomings with the ActivityPub protocol used by Mastodon and other similar services.
I think decisions like that are an active choice not to become popular.
No one owns it so there’s no team of well paid professionals trying to make it grow.
I don't post so it doesn't affect me directly. It affects where the people I follow choose to post.