Not only that even if someone could in fact generate profits by being an expert on poker or sport bets it is still not a form of passive income, in fact it is the complete opposite as you have to be heavily involved with every single bet that you make and try to predict what your opponent will do in the case of poker or how the odds will move in the future if you decide to become a sport bettor, so the dream of getting passive income out of gambling is basically impossible no matter how much I look into it.
In other words, even if someone is good or an expert in that field, they are still working and putting their best to make profits. Can't be considered as a passive income but rather, as another way of making money for these people. A passive income shouldn't be supposed to work that way as it is called passive for a reason.
Maybe the best would be, that gambling can be another source of our finances. Although still at risk, there are pros that treating gambling that way. They are still losing but the overall profit they made was already decent that's why for every loss, they can cover it. They are able to maintain their winnings in the long run making it possible for them to support their gambling activity.