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.
Oh yeah, I forgot about the set minimum amount for deposit but for withdrawals. I've seen some casinos that have changed it because in the valuation if the price of bitcoin is high, it's considered quite expensive if the price of bitcoin is high and they won't change the minimum withdrawal. But yeah, it's a case-to-case basis and in some manner, it's not usually the case for most gamblers. It just so happens that some have to experience it and the market was quite good before but now, it has changed and we're looking at the market and seems back to the bearish trend.