There not only one choice in gambling which is to lose, there is also another choice which is a chance to win. There are two chances a person will either lose or win. So 50/50 chances. But take care to start there are some experts from whom it is not possible to win.
I think the percentage of 50/50 for gambler is not the real ratio of winning and losing. Especially if you are going to be a house edge you are not going to let that percentage to happen.
Mostly what is happening is that 30/70 or 20/80 that higher ratio is always on the favor of the house edge because you are running after the profit.
And you want your gamblers to experience good gambling experience but in the end still losing.