Diminishing Returns.

Diminishing returns: each additional investment produces a smaller and smaller proportional increase in quality. That is, if you were to ask consumers to rate quality on a scale from 1 to 10, what you would find is that eventually, a linear increase in investment does not have a corresponding increase in quality. This happens even when you re-rate older products.

What follows are a number of racing games on console hardware spread roughly 5 years apart. What you will notice is that sometime in the early 2000s, arguably beginning with the programmable shader era, the graphics seem more like a commodity than an obvious necessity.

Suppose we sorted these and other video game images in random order and threw in actual photographs and movie stills. Then we asked people to rate the images from 1 to 10, 1 being "I can barely tell what this is" and 10 being "this is a photograph." Then, we plot people's ratings vs the date of the software's publication. Would you expect a linear graph? I wouldn't.

Note that the gap between the Xbox One and the Xbox is 12 years, which is roughly the same as between the Nintendo 64 and the NES.

Atari 2600 (1977):

NES (1983):

 
TurboGrafx-16 (1987):

Super Nintendo (1991):

Nintendo 64 (1996):

Xbox (2001):

PS3 (2006):

Xbox One (2013):