Probably because people use these 120fps to deliver slow motion in regular 24fps/30fps/etc timelines, so they have no need to watch/edit them as 120fps...
I understand there’s no need for it, but have you seen the size of the latest F-150?
To quote Jack Nicholson playing Frank Costello in the Departed:
“I haven't needed the money since I took Archie's milk money in the third grade.
Tell you the truth, I don't need pussy any more either...but I like it.”
> it looks almost exactly the same
What is “exactly the same” to you? And does it mean the same to me? And can we measure it?
That is not at all what I said.
> What is “exactly the same” to you?
The different scanout speeds can probably be used to produce slightly differently looking images for 30 fps content on 30/60/120 fps displays. In practice I don't think you'd be able to notice the difference between 60 and 120 fps scanout for 30 fps content.
With regards to display, for gamers, smoother scrolling and UI, and (for video) as an additional marketing specs-box checkmark for suckers. With regards to capture, for dropping in a lower fps timeline to get slow motion.
Well, because "no need, but let's add it in case some outlier is interested" is hardly the way to design mass market products (or even high-end, professional products for that matter). It's more for designing custom rigs, than anything that needs to make money...