In all given replies, it proves that the advice gambling only what we can afford to lose is not just some theoretical practice or any unproven method to keep one from being too hooked on gambling. Gambling what we can afford to lose is one of the practices under responsible gambling which is also an advice of the government and other concern individuals when it comes to gambling activity.
There are lots of stories where one person befall to gambling addiction and financial ruins because they don't follow the advice of gambling only the money that we can afford to lose. So these kinds of different people sharing the same story is a proof that the advice of gambling only what we can afford to lose is one of the best practical advice and application that a gambler must follow to avoid financial ruins.
It's hard to beat the house, gambling is a game of luck, so my answer will always be YES, I am going to keep using money that I can afford to lose, you should have ask people how much is money that can afford to lose, instead you said no one really have money they can afford to lose, you are wrong.
Even you OP has money you can afford to lose, let me give you an example, there must be sometimes in your life where you spend money on unnecessary things, those type of money are better use for investment or trying your luck.
Let me go deep into better explanation, if you are earning up to a 500 in dollars every month, how will losing $1 on gambling every week affects you? Will you be willing to take risks with $1 and still have $499 left or you willing to take risks with $60 and have $440 left? You are the only one that can answer this, some money won't hurt even if you lose them.
Still not satisfied? Ok let me use this example again, how much have you paid on gas in crypto this year alone? Why didn't you feel pained when moving $100 to exchange using $2 every time? Because it's worth it, isn't it? It's just $2.
So use those money you will call "Just" to gamble, this is the perfect money for gambling, and only you knows the amount that won't do you a thing when you lose them.
This one is a good example why people have spare money to spend and can afford to lose.