"Old School Graphics" is not equal to "Masterfully crafted low res Graphics, Like Zelda, DK, Mario, and all those nice looking classics"
It's just a meaningless marketing term. There was tons of crap low-res back in the NES/SNES days too.
Bad graphics are bad no matter what the resolution. You see poop come out of MSpaint, and you see high-res Photoshop poop. An artist is an artist, and if he knows how to draw, it shows. People look at pixel art as if it's some kind of skill different to classical drawing.
More people have access and know how to use MSpaint = Predominantly MSpaint poop.
Also, Advantages to low resolution:
Rendering a smaller area uses less gpu time: The game can run faster and do more than a high-res equivalent.
It's more abstract in general, hence can be more "realistic", depending on style. Just as a book is photorealistic (in one's mind), pixel art stays just far away enough from attempting to simulate reality, and the player's brain interpolates the heavy lack of information.
As graphics become increasingly defined (and thus, high-res), the users brain tries to match the larger dataset of pixels against the "ideals" it has for that object. Thus, any small errors in perspective, line width, shadow depth, facial spacing, add up fast, and all those non-matches equal what the average person defines as "Bad Graphics": graphics which miss so many "matches to their ideal" that they break imagination and continuous thought. "Mobile Style" High-res, like angry birds, Cut the rope, etc. Is just a high resolution implementation of Low-res abstraction, if that makes any sense to you (simple shapes and shading). That's why they all look cartoony, because to approach realism at higher resolutions is to increase potential missed matches and "bad-graphics-ness".
Achieving the maximum available realism (for any given resolution) increases exponentially as you increase resolution.