A similar thread like this was made before, the assumption comes from Minecraft, as for why, DontTalkDT basically sums it up
here
Basically this is what he said:
"The human eye works in very strange ways. Despite the eyes technically having such a large FoV if one used a camera with such a large FoV to make pictures the pictures would look unnatural for us. (See
Fisheye Lens)
For a long time there was a rule of thumb amongst photographers that a lens that produces a picture that looks "natural" to us has a FoV of around 40 degree. In recent trends that may change, though. For example the iPhone X uses a camera with a 65d egree horizontal FoV and still looks natural.
(Source: "How To" by Randall Munroe)
Not sure where 70 degree exactly came from. It's one of the OBD artifacts in our calcs. It doesn't seem too wrong, though, given the above."
"The thing is, things will be drawn or recorded in the way a camera perceives it, as the result is supposed to be a good looking picture. The result is not a visual stimuli send directly into our brain, where a FoV matching our eyes would look better.
For instance, our eyes also perceive things in a very different way regarding resolution:
However, nobody would draw a picture in the way our eyes actually see it. Everybody would draw it like a camera does."
If you have further questions, DontTalkDT should be more than happy to answer your questions on his message wall.