Online casinos limit maximum payout in games, either by limiting the maximum amount you can wager or by limiting the payout directly. The latter doesn’t apply to progressive jackpots. Limits vary from casino to casino and from game to game.
The limits come from the fact that casinos don’t want to face unlimited liability – for example if someone bet a whole lot of money and won, or if someone was incredibly lucky, the casino wouldn’t be able to make the payout without ruining itself financially. Another reason is to discourage players from gambling beyond their means.
In slot games the total bet per spin is limited through putting limits on the betting options – the number of paylines, the coin denomination and the number of coins per payline. When it comes free spin bonus rounds, where players receive payouts without wagering, there are limits too. Someone’s lucky streak can be stopped by limiting how many times a bonus round can get retriggered. There’s also a payout limit – if you reach it, you don’t have free spins anymore even if you haven’t used them all up.
Some slots and video poker games offer a feature called gamble game, where you can double or quadruple the payout. That could mean huge winnings, so online casinos put a limit after which you need to leave gamble game and go back to the main one.
There’s also an issue where casinos offer very high payouts but at the same time limit them. For example a variant of Keno where you can win $1,000,000 if you play with $10 coins and hit all 15 numbers. In reality you would only receive $250,000 because that’s the limit.