Sox and Yankees fans just care more. Rabid fans spend more money. That money translates to resources and eventually rings. This type of disparity is true in ALL sports except the NFL. Example: University of Texas has fans who are crazed for college football. They want to win. They spend mountains money on merch and devoutly attend games. College football is king in Texas, but not so in Connecticut, where we are. UConn couldn't even fill a 40,000 seat stadium the first game after poor Jasper Howard died! A player died and people don't even come to show support.
Admittedly, it's a bit of a chicken and egg thing. Were the Yankees not so successful for about 90 years would the fan base be so passionate? Hard to say. But let's look at two examples that contradict that theory. The Red Sox, of course, went 86 years with no titles and only three World Series appearances. Yet the Red Sox fans continued to come back year after year and sell out games, buy caps and shirts, and watch faithfully every night on TV (ad revenue).
Conversely, the Tampa Bay Rays, perennial AL East whipping boys, finally broke through and made it all the way to the World Series, and they were having trouble selling out ALCS games! Believe me. When contracts for B.J. Upton and Evan Longoria come up, you can bet your Yankees World Series hat that the Tampa front office will tighten their purse strings. The Rays will be back in the basement before long. Someone needs to hold these owners accountable for running teams into the ground while turning a profit, but thats a different story.
Except for the NFL, all sports are largely regional. On the East Coast it's baseball. On the West Coast it's the NBA. The South and Midwest drool over college football and NASCAR. It's about culture and tradition that's all. You care more and you get what you want for a sports product.