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.
It would've been nice if this was the case but unfortunately it's not, i've only seen a handful of casinos that change their minimums (deposit/withdrawal) based on significant price changes and the rest are always fixed to 1mbtc and above. Overall you're still forced to play with the same value unless you're okay playing with alts which usually have lower minimums.
What I noticed is that the minimum withdrawal amount goes up with the bitcoin price but never really goes down anymore. We are 50%below the ATH and it doesn't seem like the next rally will come any time soon, maybe it would be better for casinos to change their requirements again. For me it is better to gamble with bitcoins when the volatility is lower. When there are no big price jumps it's easier to leave some coins at the casino.