>>At least in gambling they don't let the sports referees and players gamble.

Oh c'mon now. This is completely impossible to police. Players and referees are not under constant supervision. They have families, friends, partners. Some of them got caught but you can be certain most weren't because it's just very difficult to catch.

There are always multiple people who know about key players' injuries, illness, other factors. The game is negative sum and additionally insiders take a a chunk for themselves. It's worse then roulette which at least doesn't pretend to be fair.