Here in Norway (and probably Sweden, too) BankID is a widely used authentication system, and most domestic services will use that as a auth / login. Only "drawback" is that it requires 2FA, which is quite trivial today. But there are still tons of users that want their "login with FB / Google / etc." . And a last but: If using such auth systems, one would have to account for all the different systems unique to countr…
A lot of people seem to agree that relying on a handful of too powerful American companies, especially in the ad and social media space, is a terrible idea and running foul of privacy requirements. Remains to be seen if some larger alternatives manage to pop up though. The European landscape is pretty fragmented.