There's a lot of seemingly purely local infrastructure that nowadays depends from networking. login calls into a PAM module, which does database lookups, which

There's a lot of seemingly purely local infrastructure that nowadays depends from networking. login calls into a PAM module, which does database lookups, which goes through nsswitch and under the covers tries to consult nscd or systemd-resolved or some such, which either have network timeouts to tick down or aren't started until boot network interfaces are configured .... Mind you, there was the same issue with NIS.