I read somewhere that it's because human eyes focus on something that is the size of your thumbnail at an arm's length, so pretty small, and that distorts things a little bit so that what we're focusing on appears larger. Whereas cameras take in the entire field of view as their focus (at least phone cameras, lenses are a whole other ballgame), and all of that data being poured in at once means the distortion isn't there.

But that could be complete bull. I just read it somewhere on the Internet and it made sense lol.