It costs a lot of money to maintain and improve a decent gambling service. The only way something sustainable that offers no edge will work is if it runs itself (smart contract) and is PVP. This will have a lot of shortcomings like the fact that users might never be able to find another party to match their bet and play against them. The margins of casinos are lower than you think after affiliate, bonuses, marketing, administrative costs, salaries. It really isn't that unreasonable that edges in the bitcoin scene linger around 1% for some pretty impressive services while normal casinos can be up to 15%.