It only increases when we feel stagnant despite that we're winning. And if we're losing, we feel that there's a need to increase that because of how it can quickly recover our losses. That's the reason why many gamblers start to increase their bets due to those reasons and sometimes, it's only about what they like to do and when they feel of betting more because of thought that they're luckier at that time. Even with a bunch of tips and reminders we give to all gamblers, we have no control over them and they'll continue to take risk whether they can afford that or not.
It is often said that we can only take a horse to the river but we can not force it to drink water from the same river, the horse chooses when, how and where to drink water, same goes for gamblers, we can only advice gamblers on what is right and what is wrong to do based on all we have been able to learn from our personal experiences, but we can't force them to adhere and or practise or do things exactly the way we have advised they should do it.
But it's always very fine since if they make their own mistakes, they will learn and have something to teach others too..
Personally I don't increase my bets on a game when I am simply gambling to have fun and not chasing after profit, increasing bets is one way to run out of bankroll fast but may also lead to the breakthrough the gambler is or may be looking for, but then, this is gambling, chances of winning is always way lower than chances of losing money.
The learning always comes once we've made a mistake and for these gamblers, they'll also learn theirs soon. If they keep on increasing and they're having some troubles of reducing it and become consistent even if they're going through a losing streak. They probably have a lot of money to lose for if they keep on doing it. The mistake comes often when they have realized that they're doing it very wrong and that's why if it's them to decide whether they should increase more after losing, that's what they have used to do.