Why not let the administrator decide?

Why not let the administrator decide?

This is more than just "best practices" altering; in the time interval between the "best practice" of password expiry being written down, and today, it's been empirically studied and theoretically analyzed, showing that the best practice neither improves security nor has the effect it is intended to have (as explained in the rationale for the best practice).

Given that the rationale for the best practice is disproved by reality, and that it's a non-trivial piece of code (as it involves date handling, which is inherently non-trivial), it's almost certainly the case that it makes the maintainer's life hugely simpler if it's removed.

And note that because event-based expiry (where an external event tells the system that your password is expired) still exists, anyone who does need a time-based policy can implement the time-based part externally, and trigger an expiration event at the appropriate time. That is more maintenance burden for them - but they're the people who want a feature that has non-trivial maintenance burdens and where research says it's a net-negative, not a positive feature.