I think what killed these services was a potential for abuse and spam. If you have your name/details attached to an e-mail account, it's super easy for marketers to scrap that, and then spam you if you meet certain criteria.
Centralised services (with all my distaste towards them) prevent that, because they block spammers, and limit access to such data quite nicely.
For a similar reason I think many people stick with gmail - because it's centralised, it can use ML to filter out spam much better than any other mailing services. It's also more secure - the Google's budget on maintaining security of their services is far higher than that of any other provider.