Why can't you compare MLB to the NBA or the NFL?
The Walmart/KMart analogy falls short on me. Those are rival businesses competing for your retail dollar. If KMart disappears (which they did), Walmart can still continue (which they are doing). If Amazon wipes out Walmart and every other retailer (which they are trying to do), Amazon won't disappear in the aftermath. But MLB needs multiple teams to produce a product. If 29 MLB teams collapse, and only, say, the Baltimore Orioles survive as the last remaining MLB team, they won't enjoy the same monopoly Amazon is striving for. Who are they going to play? Who outside of Baltimore will care?
MLB is one business competing for your entertainment dollar. It's a singular corporation, not 30 little corporations. And there are multiple corporations that have a heavily profitable division or divisions carrying several lesser profitable ones. The competition for the Red Sox isn't the Yankees. It's Netflix. It's HBO. It's MGM. It's the NBA. It's the NFL for part of the year. Heck, it's Jelle's Marble Runs if that spins your wheels. It's not other baseball teams; it's any other source that can divert your attention and ultimately your money elsewhere where you might find entertainment and satisfaction...