This is because there is the tendency to reduce stress by throwing money at the problem. Car unreliable? Got a raise? Buy a new car that won't break down at random. Now you are stuck in car payments for the next 5 - 7 years.
There's things other than lifestyle creep. For example, many families tend to increase their income as they get older. But the expenses also go up. Having one kid, vs 2 - 3 later on, or kid expenses when they are young vs. teenage years (where you now have to worry about increased car insurance, getting them vehicles, etc). And upgrading housing as the family grows. The effect is that your income constantly seems to be outpaced by increasing and recurring expenses.
So what happens is parents get into the mindset of doing without, so their kids can thrive. And when problems come up, they will sacrifice so that additional money can be thrown at fixing those problems. This doesn't let up until the kids are grown, and then you can sell the house and downsize. All of a sudden, your cars are paid off, the kids are doing good on their own (or you've disowned them), your housing costs is lower because you moved to a smaller house, which means utility bills are smaller too. This is now the point where people hit midlife crisis, they have surplus money and have pent up demand to "treat themselves" so go out and buy something expensive (sports car, motor home, boat, etc). And the tightened budget stress starts all over again.
There's things other than lifestyle creep. For example, many families tend to increase their income as they get older. But the expenses also go up. Having one kid, vs 2 - 3 later on, or kid expenses when they are young vs. teenage years (where you now have to worry about increased car insurance, getting them vehicles, etc). And upgrading housing as the family grows. The effect is that your income constantly seems to be outpaced by increasing and recurring expenses.
So what happens is parents get into the mindset of doing without, so their kids can thrive. And when problems come up, they will sacrifice so that additional money can be thrown at fixing those problems. This doesn't let up until the kids are grown, and then you can sell the house and downsize. All of a sudden, your cars are paid off, the kids are doing good on their own (or you've disowned them), your housing costs is lower because you moved to a smaller house, which means utility bills are smaller too. This is now the point where people hit midlife crisis, they have surplus money and have pent up demand to "treat themselves" so go out and buy something expensive (sports car, motor home, boat, etc). And the tightened budget stress starts all over again.