There are number of reasons why lock replacement is a logical decision. The main reason is probably because the lock is broken. Another reason may be that the lock sometimes works and sometimes doesn't, or that opening the door requires extra effort. More reasons may be that the key gets stuck every so often, or just that the lock is old and it's time to use a new and more secure lock. Even if a lock can be repaired, a lock replacement may be a better option than lock repair.