Devil’s advocate: the login requires a server, so even old versions won’t work unless they keep them online. And without support, they will be easy target for hackers.
I hate this, and honestly the best would have been to not change the logging at all. I bought a game that didn’t need a MS account to play and this change doesn’t bring any benefit.
Keeping up a server that allows migration has negligable costs for a product the size of minecraft. There is no excuse…