Oftentimes it's not that big of a difference in size, especially with modern video encoding like av1. There are many cases where higher frame rate improves viewing experience, like smooth motion (smooth movements of something, like people or things, panning, etc), heavy motion (when it's just more intense), giving the eye a little bit more to hang onto.

One particular great use case is dance choreography, so that's music, music videos, dancing videos, quite a chunk of videos and viewership. Most of music videos are gonna be released in 24 fps (a few 30 fps here and there), but there's a lot of "extra content" (tv shows, performances, live recordings, etc.) released in 60 fps, and there's some demand for higher frame rate like 60 fps (seeing from uploads of interpolated videos). 30 fps can be enough to have some smoothness to it, but at 24 fps it can become more jarring if not just noticeably choppy, sometimes 24 fps video is just not particularly great to look at in terms of literally just seeing and discerning what's going on. Sometimes things can end up looking choppy (like in daylight, at faster shutter speed, etc), or have more pronounced motion blur (which is good and better for motion continuity, but at 24 fps it can be a bit much). Motion continuity is quite important, and sometimes even made up frames from interpolation can improve viewing experience, even at a cost of some interpolation artifacts, when the end result of smoother motion is more pleasant to look at.

Of course, it can be a case of experiencing something better and then seeing things as choppy looking back (and 24 fps can really look choppy in immediate comparison), and it may not make that much of a difference if you've just been mostly seeing 24 fps video and not thinking much of it, or seeing 30 fps which is smooth enough. But in my opinion, even starting at 40-48 fps, that's already gonna feel much easier for the eyes compared to 24 fps. Sometimes there's just a bit much going on in the frame and 24 fps is not enough. Our eyes don't see in 24 fps after all. (also, higher frame rate doesn't preclude from using cinematic techniques, including motion blur and all)