take oddjobd for example, which supplants pam_mkhomedir.so in creating a users home directory on first login. oddjob is its own standalone daemon running constantly, while pam_mkhomedir is invoked only as necessary. oddjob needs dbus and systemd to complete what in many systems is just a simple mkhomedir && chown user:grp $homedir. its now fully dependent on the most fundamental building blocks of your OS to do one simple thing.
this also assumes the user doesnt have a home directory...which...many do.
in most commercial infrastructure if you suggest installing oddjobd to handle the potential for a user to log in without their home youll be laughed out of the chat. oddjobd forces organizations back into the 1980s and NIS based implementations of federated authentication where you had to go to a new user machine, or an account creation machine first if you dont want to run yet another idle daemon on your machine