Initially, bettors likely won't aim to cash out because their initial goal is truly to maximize profits with parlay bets.
But people can change their minds when they see the potential profit figures, and reading news about the remaining matches can also change their mind, leading them to cash out.
I don't think that's unusual, as every bettor has a different risk tolerance and a different amount of satisfaction.
I would also probably cash out if I saw $1000 profit rather than waiting until $2000 which is probably not achievable.