and who knows how much 1 btc will be worth by then.
right now it's $107k, but the price could double, triple, or even quadruple. (the moon is the limit really)
if someone does win the 1 btc in a year or so, it's going to cost them a lot more compared to when they added this.
Th reward structure could change by then. As bitcoin's value increases, each sat will be worth more and you will use less and less units if you are thinking and betting in fiat terms. Then it can be expected that the 1 BTC reward gets cut, maybe even in half.
Why keeping money at an exchange or casino? I don't get it. At both sites you don't have immediate access to your funds since you don't control the wallet -> way too risky.
True, but if you are a regular player who gambles every day, you want the money you play with to be in your casino account and not on a cold wallet that you have to access, sign and broadcast transactions, and then wait for everything to confirm on chain before you can start betting. The same goes for exchanges and trading regularly. By the time the crypto is in your account, that trade that seemed so attractive a while ago might have lost some of its charm.