It's a matter of upbringing. Some people have been taught to organise, plan, budget and generally make do, others have been just given things.
As an example, within my family are two sets of kids. In both cases, the parents spent the same money on their clothes when they were teenagers. However, in one side of the family, they'd say, "We have a $400 [for example] budget for your clothes this year, how would you like to spend it?" and in the other they'd say, "What do you want to get?" and when $400 was spent, "sorry there's no more."
So one group of kids had the experience of
planning and making a budget, and the other group had the experience of
spending without thinking until there was nothing left. Unsurprisingly, the two groups have grown into adults with very different attitudes to money. One lot is frugal and paying off mortgage debts on non-flash homes quickly, the other group travels more often, has fancier clothes, and will pay off their mortgage on their much larger and flasher homes with minimum payments only.
I think these are skills and habits you must learn when you're young. It's like Markos saying that he's not seen someone who started physical training after 40 who kept at it, and anyone he met over 40 who was doing it started in their 20s at the latest. As with physical training, so with money: you have to know
how to do it, and you have to be
used to doing it.
It's a social thing as well. You don't want to be the one person among your friends who says, "no, that's too expensive, I'll do without, I'll stay home tonight," etc. The old saying is, "if you have to ask the price, you're too poor for it." People turn this around to say, "if I never ask the price, I must be rich!" Not worrying about money makes them feel wealthier - even though yes, it will actually make them poorer.
Remember also that ours is a consumerist society. To
consume defines our culture as much as (for example)
to pray defined 12th century Germany. Just look at such articles as
this one, saying,
"thrift can take lasting hold of a consumer society, to disastrous effect."
People buy things they don't need with money they don't have to impress people they don't like. That defines our culture. To do otherwise would be "disastrous".
Lack of skills in how to budget and plan, lack of the habits of a more frugal lifestyle, social pressures to spend up big, and the whole culture being defined by consumption... there's no wonder that people piss away their money. The wonder is that anyone is thrifty at all!