Depends. There are sports betting platforms outside of the US that work like stock exchanges.

Betting exchanges can offer good liquidity, tight spreads and commissions as low as 2%

I do 99.9% of my gambling in the stock market because it historically is positive sum. Even with costs (commissions, fees, bid/ask spread). For me to win, you don't have to lose. Straight gambling cannot offer this.

Is it? Robinhood allows you to trade for free, but that's not the whole story. Bid-ask spreads add an implicit fee to each transaction. This is small for highly liquid stocks, but buying blue chip stocks directly also isn't exactly exciting. If you want the excitement of gambling you'd need to either use margin (borrowing fees) or options (worse spread).

If you bet on a liquid market, you will pay vig of something like 1-2%. Where I am, it is actually cheaper to bet (just think about how unbelievably fucked that is...you can see why VCs want to insert themselves into that) but in the US your trade costs are probably underneath that level all-in.