Investing to the gambling sites is not always win because they have possible that your money will lost just like what happened to op.
But I think investing to that is good because instead of playing gambling you invest your money and you possible to earn in a less risk that playing who are risk is very high I hope most of the time when people invest to gambling sites they earn money.
That is the thing about investing into casinos that many people do not realize. Now these places have house edge, which means it will profit no matter what in the long term, there is no way that they would lose money in long enough time. If you are also investing into a place that has a lot of wagering going on with their website you will have a lot more money.
If a place has 100 btc wagered there per day, they are going to make 1 btc per day on average with 1% house edge, if there is a place with 1000 btc that is 10 btc per day instead, so find places with a lot of wagering going on. Definitely that place could be hacked but so does an exchange could be, sure there could be big win whales going on, but there could be also big whale losses as well, sure some people could get lucky for a while but also they could get unlucky as well.
In the long run with house edge on your side, investors can't lose money in the long term, on average they will keep making profits.