Yes, you are right,no gamblers bet to lose money. They do it in the hope that they will win, but sometimes they are not right and face losses. However, those losses are not negligible, they are very small, and they can affect someone's balance. But when they combine, they really make an effect as a whole. There is a famous quote, Learn from your mistakes, and you will succeed, and the losses are the cause of these mistakes. So if you can't consider your losses, how can you move forward?
Every gambler must lose money at one point or the other, because gambling on it own is a high risk thing and for that it outcome is greatly uncertain and gambler's must have to settle with the fact that they gamble to lose more that they probably will gain in the end and if they win they also know that they win by luck and not basedon they skills.