But if you add everyone in the country together, the casinos win.

Makes no difference anyway. Lets say you had no tax on winnings.
You have a big win. You now have more disposable income.
Two choices......

1. Invest it, die, and someone pays inheritance tax
2. Spend it, and whoever you spend it with pays income tax and or tax on profits (assuming you spent it legally )

So one way or the other they get the tax anyway