[jasomill]

Considering the heat generated by lighting, the relatively low sensitivity of film stocks, and the relatively small aperture, uncoated lenses available at the time (1926) 24 fps was standardized, I suspect exposure requirements may have also played a role in preferring one of the lowest feasible frame rates.

It may or may not have been a coincidence that 24 divides 120, potentially simplifying the design of electrical devices (lighting, motors) powered by 60 Hz AC; I don't know enough about the technologies involved to say.