You are wrong. The profit is not guaranteed. In fact, the risk of profit is quite high for casino. However, with high risk, it come with high rewards too. Although the house edge is only 1%, the profit can be quite impressive. Someone already have got 35% profit just by investing for 3 months.
"Someone" so basically it's not the majority thing that will happen to every bankroll investors because if does then we can saw many gamblers here claiming that investing in a gambling site bankroll is really interesting.
And yes high risk comes with high rewards that's why to be able to see some good profits out of investing in a gambling sites bankroll, we need to put some decent amount. Since it's long term investment make it worth. Putting small or average amount to consider will not bring an investor to a decent profit even they have to wait for many years while their idle coins is on a certain gambling site.