Why didn’t tetherball became a famous sport like mix martial arts?
I’ve always found tetherball fun to play and fun to watch.
I am going to create a reality show with the same tournament style concept as Ultimate Fighter, but instead of mix martial arts taking place as the main combat event it is tetherball. 
Is it going to be full contact tetherball?
Are the contestants going to be nude or semi-nude?
In pertty much every game of tetherball I remember playing, the server would serve it so that the arc of the ball would always keep out of the opponent’s reach. Has anyone ever developed a set of tetherball rules that would prevent this, and make the game (a) playable and (b) something that wouldn’t result in rallies that could last hours?
The same feature that makes tetherball a good participatory sport also makes it a bad spectator sport. It doesn’t require much skill, so a group of random kids on a playground can all play it together and all have fun. But that same lack of skill would make competitive play much less interesting.
I had to google it as it is pretty much unknown in the UK. We do have swingball which is much the same but a smaller ball and using racquets. Not a great sporting spectacle either way.
Modify the rules. Allow use of the feet as well as the hands and make scores higher for foot techniques. Institute a “foul zone” above which the ball cannot swing. Make sure the athletes are attractive and scantily clad and accompany the matches with pounding rock music and a lot of lasers and pyrotechnics every time somebody scores. People watch soccer FFS.
I basically agree with the OP. There are so many stupid sports filling the airwaves in between Super Bowl of Ads and the nearly endless basketball playoffs that it seems like someone should have professionalized tetherball by now. No gimmicks, maybe just a taller pole and some basic rules about valid serve zones and such. Scanty clothing optional.