Because 60fps and 24fps don't look alike and video shot at a very high frame rate can look off to an audience.
Remember also that typically a 1/2 rule is followed where the exposure of each frame is half the time of its display. So for each of the 1/24s intervals, an exposure is made for 1/48s. A shorter exposure would have less motion blur but look jittery. A longer exposure would look too buttery. People are extremely used to 1/48s exposures displayed for 1/24s (or similar).
48fps video in the Hobbit movies was very negatively perceived. It looked too much like a video game.
You're in the minority, I think. The Hobbit was shot in 60fps and most people found it very uncomfortable to watch. It felt like you were watching a movie set rather than a movie. Suspension of disbelief is pretty important for cinema and 60fps really messes with that.
I also think most jerkiness in 23.976/24 is due to incorrect display settings leading to dropped/skipped/repeated frames. If your display can match 23.976, even panning scenes look pretty smooth. It's the jitter that messes with our brains and looks bad.
It's not jitter that bothers me, it's the stop motion effect. It's especially bad with action sequences that have a lot of closeup shots.
This is basically every movie with any sort of action in the past decade or so. If you do closeup shots in on some fast action in 24fps you don't have to worry one bit about choreography, since it'll just be a choppy blurry mess and nobody can tell what's going on anyway.
I can agree things like sports are a lot better at high frame rates. You want to see what players are doing precisely in a live setting. But people don't watch sports in movie theaters.
I'd argue stylistically the lower frame rate works a lot better on a big screen. There's also the fact that high frame rates on a big screen seem to cause some people to get motion sick.
I personally have no issue w/ action scenes which are shot at 24fps. Yeah, there is a fair amount of blur but it all seems natural (at least on a cinema projector), and conveys the fast movement, even if it might not be precise.
Take Jackie Chan's Drunken Master epic final fight scene for example - yes it's a bit blurry but I can make sense of everything going on. If anything it enhances the feeling of action - if this was shot at 60fps, it would look much more "real" and be a lot less enjoyable.
There are always a lot of unsatisfying hand-wavy answers to this question just saying that high framerate video looks "off" or "like a soap opera". I'd like to point out that the biggest factor here is probably the lighting.
Cinematographers have to pick particular aperture and ISO to get the depth of field and film grain they want, so they can only really adjust exposure though shutter speed. If you double the framerate, the minimum possible shutter speed halves. Therefore (unless you are shooting outside on a sunny day) it is very likely that your shot is underexposed, and the only thing you can do about it is add more lighting. This can be both logistically complicated and technically very hard to pull off without looking unnatural, especially in scenes that are supposed to be dark and moody.
I wonder what the viewing experience would be like if it were shot in 48fps, but then most alternating frames were dropped so it still felt like 24fps, except for certain key visual sequences - action, big effects shots, etc. You could even transition between the two frame rates over a few seconds.
As others have said, 60fps can actually look "off" to some audiences. It definitely looks "off" to me, and I can't quite put my finger on it/why. It could just be my age (late 30s) and my brain grew up on 24-30fps.
Many new TVs interpolate 24/30 fps to be 60fps. This is knows as "The Soap Opera Effect", and has been written about here before. [0].
To me, 24/30fps feels "smooth", almost "buttery". 60fps feels crisp. 60fps feels almost too real. It makes it more difficult for me to suspend disbelief, whereas 30 makes it easier to suspend disbelief and get lost in the imaginary world that's being presented to me as if it were real. It's really difficult for me to explain....
The horrible "motion smoothing" interpolation is the first thing anybody should turn off on a new TV. I absolutely hate it, just ruins the look of movies!
I've completed a video shot at 24fps, some footage was recorded at higher frame rate for slow motion, but you can tell the diference. The 24 fps is the best, as it looks and feels better in the eyes for most people and also my audience :)
Remember also that typically a 1/2 rule is followed where the exposure of each frame is half the time of its display. So for each of the 1/24s intervals, an exposure is made for 1/48s. A shorter exposure would have less motion blur but look jittery. A longer exposure would look too buttery. People are extremely used to 1/48s exposures displayed for 1/24s (or similar).
48fps video in the Hobbit movies was very negatively perceived. It looked too much like a video game.