Why would you ban gambling and not allow online casinos in your own nation if you do not want gamblers to lose money to other nations? If you want them to actually give you money instead of take money out just start casinos and reap the benefits? In any case USA is certainly a weird country when it comes to money, they don't even care about long term profits as much as they care about short term ones, they built the whole country on "make money now!" promise.
So, roobet can't really stop anyone from gambling, it is technologically impossible to stop anyone from gambling, all they can do is offer their advice and warn them not to play but in the end if you want to you can play here, all the while you take illegality into consequences and realize it may not end up nice for you. By the way, 90%+ of the time if you don't get reported by someone, nobody would really know you gambled somewhere, so be quite about gambling online if you are from a country where it is illegal.