One of the main reasons is the fact that most of the people buy these tokens buy it to bet with it or use other gambling benefits that could come with holding that token and not to take some profit from the swings, probably most of them don't even check the token price that often, so holders of their tokens are mostly indifferent to price decrease and less likely to sell out of panic.
Actually because of the reasons mentioned these tokens are great buys (if the gambling website is reputable) on the dips as they're less likely to not recover from the lows, since the demand is almost always there and because there are some people waiting on the sidelines waiting for those dips to buy the tokens to bet with.
I believe most of them are for the benefits of it and then next to it is as an investment. If you're with that casino that has their own token and they're offering some good percentage for having their token and some bonuses, you'll be enticed to buy it. That's why many players do exchange the cryptos that they're about to play into their native tokens.
And it's because of the benefits and bonuses that they offer for those that own it while they play. As they take those benefits, the biggest one is they're able to have a share of that casino and earns dividend just by holding and staking it on their own platform.
While having those tier or level programs that they have.