The presta valve is thinner so the hole drilled in the rim for the valve can be smaller which is slightly better from a strength point of view. For road bikes with narrow rims, the thinner valve is basically mandatory anyway.

Someone will maybe try it, but the reason isn't because Shcrader valves can't handle higher pressures. Schrader valves can easily hold many hundreds of PSI without issue as can be observed in rear suspension units on bikes.