Bitcoin price increases made some people think more about use bitcoin to gamble because they see they can make a big profit if they can sell bitcoin at a high price.
It's not about how big the profit might give but it's about the quantity and the little that they can gamble due to the high price of bitcoin. For example, when the price is at the peak, you can actually gamble with a few decimals and that valuation for that quantity is already quite good enough. That's the reason why if the price of bitcoin is high, there are gamblers that are choosing to gamble with bitcoin for such an amount. Because the advantage is if they've been holding bitcoin for so long, they have little to spend for gambling and it won't lessen a lot with their holdings.
They prefer to secure their bitcoins when the bitcoin price is at its peak, selling it will be more valuable or good for him than spending it in gambling. There is nothing wrong with their choice because it is their right to use bitcoin for their own purposes, because gambling with crypto can not only be done with bitcoin alone, there are many other cryptos that can be used in crypto gambling and it would be good to keep making their bitcoins keep it safe as an investment.
If someone wants to gamble with their bitcoins, tell them to sell it and then gamble with the cash. You cannot stop people who want to spend their bitcoins for gambling and tell it that they should've sold it instead. If the choice as they want to gamble is bitcoin then it should be made by them in bitcoin and they're comfortable using it. Although some may say that it shouldn't be bitcoin that they must use because there are other options for cryptocurrencies to be used for gambling. But that's it, the higher the price, the lesser bitcoin that can be used. Anyway the price of bitcoin has decreased a lot and one can choose to gamble with other altcoins that they prefer.