Over time, your Wi-Fi password gets shared more than you expect – guests, neighbours “for a day,” helpers, maybe even old tenants or workers. Some of those people move away, some change jobs, some you lose contact with entirely, but the password stays the same.
Changing it once in a while clears out that invisible list. Only the current family and people you want connected get the new details. It reduces the chance of someone sitting nearby and still using your network without you realising.
It also protects you from basic misuse – someone downloading dodgy stuff or accessing questionable sites using your connection, which is legally in your name. It doesn’t have to be every month, but an occasional reset is a sensible digital hygiene habit.