You can keep calling it "predatory" or "little gotchas" or whatever else you want. The bottom line is it's extremely common among online casinos. I play in many different casinos and this is a very common rule. Seriously, get the fuck over it and move on.
To continue my analogy: pretty much every bank re-ordered transactions at the time (and many still do) to maximize their overdraft fees. That however doesn't make it right.
But seriously, you honestly have absolutely no sympathy for someone who didn't know and made a bet that their software accepted? And then lost all their money ($8k USD in one particular case) for no reason, than a stupid arbitrary rule that their software should be checking (it's literally 1 line of code). But hey, that's fine because you read the thousands of words in their ToS and knew to avoid it.