A possible explanation is that acetate base is typically thicker and heavier then nitrate base. If you are using 35mm film at 60,000 frames per second, the film is moving at a mile a second. I believe they had a blank header that was several hundred yards long just to get the film up to speed. All the film had to be wound off one spool and onto another. The spools would have large cores, so you did not have to violently accelerate the emptying reel, while braking the filling one. Anything that would make the film lighter and thinner is a bonus.
There were custom emulsions too. There was one with three black and white emulsions, with sensitivities in the ratio 1:100:10,000 so you could capture exposures of a million to one with constant aperture.