“In tennis you cannot kick the ball. In swimming you can't try to pull the other guy down. Its just the sport it is.”

Was kicking the ball ever legal in tennis? In swimming was it EVER legal to pull the other guy down?

“Why don't boxers throw? Cause its boxing”

Again same thing has throws ever been legal in boxing?

But in Muay Thai were throws legal at one time or another? But they aren’t legal now?

This goes to what Lkfmdc wrote

“I can throw you over the inside of my leg, but not the outside, uh, OK?"

It’s like the swimming example. You can’t pull the other guy down. BUT you can if you pull him over the inside of your leg but not the outside.
Logically it makes no sense. If you can do one why can’t you do all. But these are the rules if you are going to participate you just have to go along with them.
Just like in San Shou when people always say “ Why throw it’s stupid if you can’t follow up with ground work” It’s the rules of the SPORT.
But it would bring a different view if throws were illegal in San Shou and they just added them.