With money you don’t want everything to be as divisible as possible, you want everything to be able to be put together with as few pieces as possible.

So 20 is very useful, 120 not as much.

60 Hz power is the rare good call over European 50, though. Gets you 60Hz television as a standard and even though modern displays don’t care about the frequency of power as much that eventually gets you to 120Hz displays, which is super useful to support tons of display frequencies on even intervals. You can finally get evenly paced 24fps movies again.