Meanwhile clubs like the Orioles only fill the park when those two teams come to town, whereas when they were competitive, Camden Yards was filled with Orioles fans. Now they, and many other clubs, have been reduced to begging for crumbs.
The Boston/NY nexus of baseball interest is eroding interest in many other markets, to a greater extent than those two markets alone can replace.
Its media focus, and marketing. The Cubs have almost as much of a national following as the Yankees and Red Sox, primarily because of the their formerly ubiquitous presence on WGN on a national cable market. Combine this with the "charm" factor or marketing both Wrigley Field and the "Lovable Losers," and you have what is arguably the most popular team in baseball west of New Jersey. And while the on-field product for the Cubs has been markedly improved in recent years, no one would put them in the same competitive circles as Yanks/Red Sox.
The Cardinals are also very, very popular because they have traditionally had a radio network that brought Cards games to anyone who wanted to listen in the midwest. They still do.
The Yankees and Red Sox have the money to spend, in part, because they also have massive, revenue producing broadcast outlets.
Teams like Kansas City and Pittsburgh are doubly cursed, being in small markets and having very little opportunity for media exposure. Perhaps if teams like the Royals (or the Nats, for that matter) could become competitive, they could generate enough to begin to lay the foundation for more marketing success. (Recall the salad days of the late 70s and early 80s for Kansas City and Pittsburgh).
Things will not change, however, as long as the Players' Union holds most of the bargaining clout, and as long as all 30 teams continue to make money.