> Also, why can't I sign a paper saying I accept the risk of investing?

You can! All you have to do is lie on your affadavit of accredition, granting you the two things you want: (1) investment in the venture, to (2) no ability to file criminal charges on the venture management if you get fleeced. You do want both of those, right?

FWIW, in most of the US gambling is illegal and lotteries are often regulated by the State.

There's loads of casinos though:

https://www.worldcasinodirectory.com/united-states/map

And aren't states mostly the beneficiaries of lotteries? Here the revenue is supposed to go to schools or something.

That source is pretty questionable. I'm pretty familiar with Texas' gambling laws so I was surprised to see so many "casinos" in Texas. Upon further review, many of those points are improperly placed, with actual casinos being out of state but simply matching a partial address. I'd take that map with a massive grain of salt, as chances are a high percentage of points are probably wrong. Of the three casinos near DFW, two are out of state with the third being a horse racing track. The one outside Austin really exists in Indiana. It also shows cruise ships, which usually don't begin gambling until they're well offshore.

I'm not going to deny there are many casinos (there are plenty) but the OP's statement of "gambling and the lottery would also be illegal" seems to miss that in probably the vast majority of the US, gambling and operating lotteries is illegal. For example, Texas recently had to have a constitutional amendment to allow sports teams to hold charitable raffles.

https://ballotpedia.org/Texas_Proposition_5,_Definition_of_P...