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.
I discussed this recently with a friend. Commercial gambling, e.g. slot machines, online poker, F2P mobile games, sports betting, etc. seems like exploitation of weak people. These products are carefully optimized for return of investment, which always means nudging people to play more, even if it’s bad for them. This book is pretty good: Addiction by Design - Machine Gambling in Las Vegas