To be fair the sport of MMA is entirely different. You’re only dealing with one fighter as opposed to a team. The UFC has had a plethora of fighters test positive, but they can just cancel the fight or replace the fighter. Team sports don’t have that luxury.
Having two or three fighters on a card test positive isn’t that big of deal, even when the UFC lost their main event title fight due to the virus it didn’t hurt the card. In a team sport losing two or three players to the virus would be devastating for a team’s competitive chances.