Could be in any context. I do it a little on UFC fights but that’s a relatively low amount and I can afford I to lose any time I do. It seems like it’s becoming a really wide spread problem though, at least in the US. At the same time I don’t see why it should be illegal. Granted I also don’t think any drug should be illegal.
Except that the payout for those bets are generally done so that the house takes a cut of the overall action. The vig is baked into the payout for sport outcomes; betting on all the outcomes equally isn’t going to probabilistically give you the payout equal to what you’d buy in.