Early film cameras were hand cranked, so the actual speed of the film was all over the place. I assume it was just too much of a hassle to manually correct the speed of these films, so they didn't bother.
As an anecdote, I remember when I was a kid (early 80s) my uncle who collected old cameras and projectors exchanged with me an old hand cranked pathe-baby projector for a solar powered calculator. The projector was working properly and had a few films cassettes and they were supposed to be played back at variable hand cranking speeds according to the scenes. It was an interesting experience to play those films back to my family in the only room that had absolute darkness, in the kitchen.