So using your example, maybe there is something at the top floor that needs guarding. Someone manually pressing the elevator doesn't fix this, he becomes another weak point that can be easily socially engineered. One alternative solution that doesn't require that bullshit job is a separate elevator with its own lock/access, which is a very common solution used in many buildings.

I don't understand your defensiveness here. The entire point is to question the role as a solution to the problem. Literally what bullshit jobs is all about. This isn't specifically about the elevator man, so you don't need to get all weird about it.