24 fps is the standard for cinema because that gives the preferred look for most content, with nice looking motion blur and whatnot. High frame rate may make sense for some movies, but it's not a win for the whole industry to go 48 or 60 or higher.

I'm not sure what you're getting at with the 120 fps comment, because that is obviously not the frame rate of the finished product, so it's not the same conversation.