Residents to elect their own mayors?

Someone suggested this to be a better thing. My question, why do we need
mayors in the first place? To give more pay to the mayors? What can the
mayors do that the MPs cannot do or vice versa? Oh, MPs are part
timers, too busy working and making money. Are mayors part timers also?
If full timers are needed, why not make MPs full timers? $16,000 pm is
not small change and deserves to have a