Is there? What's the downside? It really only effects a relatively small group of highly compensated professionals who accept it as a condition of employment. There's basically nothing to lose by making this the rule, but it could prevent some scandal that damages the league.
The downside is unnecessary restriction in peoples' lives, and shit like 41 game bans for role players who probably can't afford to lose their livelihood over betting on tennis or cricket or whatever unrelated sport they get busted for. Or maybe some NHLer makes a side bet with a friend on the Super Bowl like millions of other people do and gets ratted out and loses his job.
Does that seem like a fair punishment?
If you allow players to bet on their own teams, or sports other than their own, you have to be able to police that and separate the legal bets from the illegal ones. I think this is achievable with the technology available on an account-by-account basis.
There is also a stigma about athletes gambling but in some, like golf, it's expected. I don't think this is anti-scandal so much as it is anti-gambling and anti-vice, like drug suspensions. Pro sports leagues don't want sob stories about players losing their millions on traditional "vices" like gambling, and only THEN maybe fixing matches to pay the debts.
That's the only rationale I can see and it's honestly not that likely imo since any of these players can just as easily go to Vegas or some other legal gambling establishment and lose that same money at a cards table or whatever.
At the very least make the punishment fit the crime. 41 games for betting on the plinko game during Price is Right is not where we need to be.
