Sportsbetting is a skill based gambling which is why it is relatively easier for people to make money in it.
Many casino games are luck based which is why it becomes harder to win since our luck doesn't always shine.
But it doesn't mean that we cannot make more money in casino games.
But there are also other casino games which are skill based such as poker in which many people do make money.
You just have to be better than your opponent to win the game.
I can agree with you, that you can win a lot of money with poker and blackjack if you really know how to play it. But for all the other casino games (such as slots, dice, limbo, mines,...), there is no real winning strategy, in the end you will always loose money but there will be some people that get extremely lucky.
Right in skill based games you have chances of winning against the people or house if you master those skills and have knowledge how to make next move and can win according to that.But luck based games don't have anything to with your skills and you cannot apply any strategy also so both have different working.