The Yankees used to have classy fans--and still do have many. They are a rich, classy organization. Their AAA ballpark in Scranton reminds me of Yawkey's old Fenway. Spotlessly clean.
What's changed things is cable TV, the critical importance of TV revenues in sports, and the dominance of NY as the major TV market. You now see a predominance of NY teams in network cable games, including MLB.com. That's because the advertising revenues are greatest for the NY market. ESPN , for example, is basically a NY cable station. And a lot of the mediatalk is about the Yankees, Jets, Knicks, etc. Check out the Globe which, by the way, is NY-owned(NY Times--which also owns a piece of the Red Sox). And then you have the major sports drafts, which are mostly held in NY and dominated by noisy NY fans wearing their team shirts.
The NY fans know all this--they know their teams are the "media" teams--and it has just bred a lot of arrogance into the new generation of NY fans.