It is the fact that hardly to accept for gamblers, and it is really easy to understand.
If gamblers win more than gambling sites, how gambling sites can survive over time and pay for gamblers.
Bitcoin is finite as well as funds of those sites.
About the losing money side, casinos do tend to win more often than the gamblers, there is absolutely no reason to be sad about that, only calculate your time and money "spent" and spend money that you are comfortable with per hour, for example 10 dollars per hour on gambling is cool with me, so I gamble 10 dollars per hour and have super fun and it always worth it. That is why I never say I "lost" money here I say I "spent" money here.