Or the people who say that are obsessed with subtlety and want everything to conform to the Western standards for art due to cultural hegemony brainworms? Sometimes I feel very guilty for engaging with this sort of media instead of something more "serious"
Seriously though the other reason for the apparent difference is simply about centuries of sifting thru mass culture to pick the stuff that's had staying power. It's like, pulp entertainment has its place and some things transcend it, but you only really know which things were "art" (a loaded term of course) with time.