OK I will play devil's advocate for a sec.
Mastodon doesn't have a large development base, only a handful of unpaid volunteers. Release cycles that also contain features requested by the community are incredibly slow and ultimately get selected by one person.
Only speaking about Bluesky because it isn't owned by one single billionaire, and is run by committees built from decent sized investors. Because of said investors there is a larger development base which leads to quicker release cycles that produce features requested by the community.
Speaking as someone who runs a single user instance on Mastodon and another on Bluesky. The latter is hella cheaper to operate because it requires less resources per user.
Mastodon is kinda clique based and requires you follow accounts or hashtags to make it work. Not a bad design, just slow to show results.