when have we ever defined gaming/gambling as 'a thing where the house takes a rake' ? I don't understand this argument and it always feels disingenuous when brought up.

I'm not really sure what position you're taking but taking a rake can certainly change the legality of an activity; in California, playing poker in private is considered a social game and is legal, _except_ if party is taking a rake.

Legally, they have to disclose all their probabilities (under most regulatory regimes).

Er it's not. Gambling where the house takes a cut is considered a form of commercial gambling and is often made illegal or has stipulations applied to it.

If you're asking about why prediction markets fall under the CFTC, this is actively evolving but generally prediction markets are considered to be under the CFTC because they can be used to hedge against events.

For example if you're trying to do business in Oman but you're worried about Iran tensions spilling over, you could take a Yes position on an Iran conflict bet as a hedge. You may lose business but can make some of it up in the hedge.

"Gambling" the concept legally is very complicated and has a lot to be understood, so I'd suggest doing some searching or LLM asking if you want an intro on philosophical definitions or the legal landscape.