It depends entirely on what it is. Chevrolet is not the only manufacturer or seller of automobiles. If they were, I would be upset if there were only one place to buy one.
There are a lot of these partnerships and contracts around, but they aren't as prominent as some of these sports deals.
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?