So what if they aren't as prominent? They certainly effect your life a lot more.
Back to your car analogy, though there are many other car manufacturers, only Chevy sells the SS brand. If I want an SS, I have to buy a Chevrolet. There are plenty of automobiles that will get me from point A to point B; there is but one SS, and it belongs to Chevy--which sells its products exclusively through Chevy dealers, which have exclusive territories, into which no other dealers may sell Chevrolets.
Along those same lines, there is only one Major League Baseball, but there are options for sports entertainment out the wazoo. There is minor league baseball, there is football, basketball, golf, hockey, curling, horse racing (TVG), etc. etc. Each of these sports will entertain a person. So there are general competitors to baseball, just as there are general competitors to Chevy, even though Chevy owns the SS brand. But you're ok with Chevy having an exclusive distributorship chain, but not OK with MLB doing the same?
I understand what you're saying, but MLB would be literally preventing millions of people from even being able to watch their games by this. Also, as I said, there is no alternative. The SS analogy doesn't work for me because there are no similar products. I would equate that to a player in MLB - possibly a team at best - but not the entire league.