50 Hz is a lot easier to math (50 Hz = 0.02/s, 60 Hz = 0.0166666). Don't know if that's why, but it very easily could be.
Is the fact there are 360˚ (2π radians) in a circle, and 60 goes into that cleanly, of any use?
So, even messier for dealing with than, say, square root of two (irrational and algebraic) or square root of minus one (algebraic).