You have an really insightful perspective on beginner's luck. I have also experienced this that when i do not have any stress and no pressure of winning, I would usually win in gambling. Although no logic fits in this as why it happens 
Why is it that when we are more relaxed and have no goals, we tend to win more ? The moment we think that we must need to win, we start to lose. Also it is strange that once a gambler is new he has less knowledge but with passage of time he starts to grasp the game and its mechanics, then he shift into a more goal oriented mindset but only to add pressure on himself. The anxiety always lead to loss.
I think you might be onto something here, because at least it's not happening just because we are new customers. Some people might end up thinking that casinos are paying more to customers that are new. Why is it that when we are more relaxed and have no goals, we tend to win more ? The moment we think that we must need to win, we start to lose. Also it is strange that once a gambler is new he has less knowledge but with passage of time he starts to grasp the game and its mechanics, then he shift into a more goal oriented mindset but only to add pressure on himself. The anxiety always lead to loss.
I used to think there was something to it, when i noticed i was winning often when i was just changed a casino. But soon after i realized that i was winning with slots, which aren't operated by casinos, but third parties who didn't care if i was a new member of some casino or not. Nor they would even benefit for promoting new casinos.
It's just a confirmation bias that only happens when we do take risks. We never notice when we actually don't have more luck as new players, or then we brush it off as nothing, because we rather believe in such thing.