The odds are manipulated to give the gambling company the advantage. Big winners are identified and dropped. It is designed to drain money from gamblers.
Stocks are not that, in general. A particular fraudulent investment could be that. Crypto investment comes to mind.
You don’t need to even win to get banned (limited from making bets larger than a couple of dollars). You just need to make bets that look too smart and might result you winning in the future.
https://youtu.be/XZvXWVztJoY?t=667
Sports betting is just looking for chumps that have little to no chance of winning.
I’m not sure what you mean by odds being manipulated. The bookmaker will generally adjust odds to where the money is being placed. Example, in American football if a team opens up as a 7 point favorite and betters put more money on the underdog than the favorite, the line gets smaller so more will take the favorite. Generally the opening line is what the book will think half the betters are willing to place on the favorite, and half on the underdog. Doesn’t always work out that way which is why you see lines move.
Also not sure what you mean by winners
Listen to season 4 of Michael Lewis' podcast. He covers the downsides in detail.
https://www.pushkin.fm/podcasts/against-the-rules
I think this is the ep that gets into the most detail, but I haven't read the transcript.
https://www.pushkin.fm/podcasts/against-the-rules/vegas-spor...
IIRC, if you're too professional or too lucky, the betting apps will restrict you and then lock you out. They only want the dumb money playing.
> Also not sure what you mean by winners
https://www.vegas-aces.com/articles/how-betting-sites-limit-...
Various forms of this have been practiced in traditional casinos for almost a century with increasing sophistication, it’s a well-established art by now.