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That's... making them lose out money though? I mean sure, if you missing the cashout was their fault then maybe yes, there's some reason to it. But no, it was YOUR fault that you missed the cashout option, with whatever reason it may be. It's implemented in trading imo because of how fast the market can move at times and exchanges don't necessarily lose out that much due to the sheer amount of volume of trades that happen. In casinos though? They look at each match as a single instance. So setting up one for each instance would just invite losses for them imo.
And to add, trading is you competing against other traders, a zero-sum game. Last I knew, gambling is you competing against the bookie, not other players.
Cashout has been very useful to gamblers especially when you don't want to wait for the game to end before you take some profits. Although sometimes we make the mistakes to cashout early in prematurely which could make us angry when we noticed that the bet finally end up in profits and we have already taken the cashout. Casino want to make money from their customers while gamblers want to make profits from themselves. Things have to work in one side whether to the favour of the casino or to the customer trying to earn profit from the game. Everyone wants to make profits from betting by all means that's why we keep seeing gamblers trying too hard to make a living betting.