Most apartment locks and such are made for the purchaser to be able to easily and quickly re-key. You set it to be rekeyed, put a cut key in, and then lock the key pattern for it in place. Takes like 5 minutes or less. That way every time someone moves out you can keep things secure without replacing the lock.

In your case, the building manager was just a lazy fuck.

It is common for lock makers of normal locks to do production runs of just like 50 different key sets.