No gambler treated gambling as entertainment all the time he is playing, there will always be a time of changing or shifting your mindset, we are tempted to be like that, we are just humans and tempted to be greedy especially when money is involved.
It's mean your self control skill is bad and you need to think what's the reason your mindset is changed. I was a gambler who gamble for money, but mostly I didn't achieve my goal and I'm not happy with the result. After that I learn to change my mindset to gamble only for entertain, regardless of the outcome is, I always happy since gambling is fun. Until now my mindset is never changed and gamble is always to entertain for me.
There are very few gamblers who think like this. The majority are the ones who are looking for money in the gambling. Others who say that they are here in gambling for fun, do not mean this by heart as at the backend of their mind, their motive is also to earn money from this industry. It is the few people like you who are very clear in their stance on whether they are in gambling for to gain money or to have fun only.
Believe me, if you decide clearly that you are playing for fun, you will realize that you will win more than those who only play for money. This is some science which I also can't understand, as to why this often happens.