Gravity feed has a very good pro: Simplicity. ON or OFF. No problem with misfeeding.
Con: Can't balance fuel, can't run different fuels in different tanks (Would Sir prefer Avgas or Mogas?)
Like Ghengis says, it's not so simple with pump supplied sources since the pump suction will thry to suck the least resistance hence single source selectors. Can't see why a balancing port between the tanks wouldn't fix that though.
Maybe they expect everyone to fly continually slipped so one tank drains into the other which then overflows?
Some high wing types had the best of both: OFF, L, R & BOTH.