Games and even films are different than reality.
When people say it looks 'smoother' it's because our eyes see movement as unnatural because of subtle imperfections on the screen. That includes everything from latency, to motion blur, to color bleeding caused by how image displays work. Higher framerates and resolutions cut down on that, which is why 60fps and even 120fps images have a higher visual quality over 30fps and why 1080p and 2160p look different to a lot of people.
It's not because our eyes see things any better on the display, but rather because the display sees them better and is able to show movement in a smoother and more natural looking way.
The Hobbit had a framerate of 48fps. I saw both versions in theaters and there was a noticable difference from 24 to 48 fps. The image looked crisper and actually a little too good. Some of the special effects were spoiled and the lighting often looked different by the higher framerate because it looked too natural. Smoke that looked much better in the lower framerate version of the film looked more like it was being puffed out of a smoke machine and seemed more artificial in the HFR version. The lack of motion blur in some scenes made the action seem slower and CGI effects stood out more.
Biologists don't have a complete understanding of exactly how the eyes work. We know the basics of course, but there are a lot of subtle things that we can't quantify and don't fully understand about vision.
I can see a difference in a 120 fps image with a 2160p resolution, but it's not because I can see more details. Movement is smoother looking and there is less motion blur. Colors also appear different in higher resolution displays. I mean outside of simply being calibrated differently as well.
It's got to do with how projection displays work and a bleeding or color blurring effect rather than any sort of fine detail that is imparted by the higher specs for the display. More tiny dots means more accurate color display even though we can't see the individual microscopic detail of fabric weave on a linebacker's shirt or individual pixels on a texture. We can still see subtleties in regard to how color is displayed on a higher resolution screen.
Put simply, high framerate and resolution displays look better more because of subtle, unnatural looking imperfections the images lack rather than any finer detail added to anything or extra frames of movement the eye can see.