The point of the HTTP verbs is to communicate expected behavior. While a server could treat POST, PUT, and PATCH the same, the point of having the verbs at all

The point of the HTTP verbs is to communicate expected behavior. While a server could treat POST, PUT, and PATCH the same, the point of having the verbs at all is to give a standard way to signal clients what is going to happen. While a server can ignore the expectation, it doesn’t mean the expectation isn’t valuable; it allows conforming implementers to communicate what is happening using standard language.