Why do most commercial airplanes use hydraulics instead of electric/servo motors?
I'm sure it's possible to use servo motors to get precise control of the ailerons, elevators or the rudder.


No, it isn't. Primary flight control actuators require both rather high forces and quick response time. Electric motors can provide either, but both at the same time is a problem. Hydraulics is still better for that combination.

Note that other actuators that don't require the fast response time (like flaps, gear or horizontal stabilizer foreplane (elevator trim)) are electric in some aircraft.