I hate to be the one to break this to you, but servers cost money. Developers cost money. Bandwidth costs money. If you want to run a reasonably successful social media company, you need money.

Bundling domain registration (already a thing) with custom usernames (already a thing) and taking a profit from that transaction is not enshittification. Enshittification would be if they took away the ability to link your own domain and required everyone to buy domains through Bluesky. This would just be giving less savvy users the ability to link a domain to their username without having to learn DNS.