Honestly, who plays 0.25 btc hands on blackjack? That is literally 2.5-3 thousand dollars each hand, that is a huge whale move if I have seen one, normally in real life you sit on a blackjack table and you will realize the biggest is usually 50 bucks per bet, I rarely ever see a person betting anything more than that, keep in mind this is a regular casino blackjack table, not Las Vegas big 5 star hotel with insane entertainments type of table, which means this dude is betting so much that if he cashed it out to dollars, go to Vegas and bet on blackjack he would be treated like a huge whale even there as well among all other whales. If you are attracting that type of customers to just sit at home and gamble on a website than you know you must be doing something right.
If you think that this is a big amount, then you must be wrong because there is more than just 0.25 btc play on stake. It is a big amount for us but this is just some tiny pennies for big whale so it does not really looks big for them. You should checked on their few pages back there when someone bet huge amount and got profit here. It seems that you are new to gambling industry that makes you amaze on this kind of bet

0.25 btc per hand on blackjack actually very high amount and i'm sure it was not all in bet which mean the players playing with plenty of bets use 0.25 btc for every hand and imagine if the players playing 30 times bets or more with it then i'm sure this players can be called as the whales in online gambling industry
I can make an assumption here that he is indeed a middle whale, because there is no way that I could bet 0.25 btc per games. This is too much for any normal players here. They can even bet this huge because of it is stake, I do not think that someone can bet this huge amount randomly on other sites. It must be really painful if they do not get paid. But on stake with really huge bankroll and with the same roof as primedice make this possible

Its pretty much no different than any regular casino. Most of the people that go to a physical casino usually gamble a few hundred, maybe less than 5% or even 1% or so gamble in the 5 figure range.
Most people usually get paid on a Friday and blow their entire paycheck by Saturday. However the casino maybe makes $500-$1000 off those types of players. When some rich businessman gambles its usually in the 5 figure range and they usually have a special room for those betters. And it comes with huge perks whether they gamble or not. From what I heard they get a free hotel stay, free dinners and free excusions.
The casinos most revenue however is from the 95% that gamble less than 5 figures, because there are many of those people and since they are mostly gambling with scared money, they usually are greedy and fearful and the casino makes a profit off them. Someone who bets in the 5 figure range usually has a net worth of 7 figures and they gamble without greed or fear and usually end up winning, if not they do it for fun.