A part of the reason has to do with the advent of money.
Money has blurred the line between needs and wants and between necessities and luxuries. Because of this we tend to want more as the line of "enough" is fuzzy and obscured.
How has money contributed to this situation?
One of the things that the Skidelskys point to is how money has shifted us away from use-value to exchange-value. Prior to modern economies and the ubiquity of money value was determined by use. The question wasn't "How much does something cost?" but "What is it good for?" Value was tied up with function. A shovel was valuable because it helped you dig. A bucket was valuable because it helped you carry things. And so on.
When use-value governs our imaginations the question "How much is enough?" is easier to answer. For example, how many forks do you need? How many cars? How many shoes? How many chairs? How many lawnmowers?
When we ask about use-value we get a sense that there is a reasonable answer and a limit to how much might be "enough." We don't need 100 forks or cars or shoes or chairs or lawnmowers. How many lawnmowers is enough? Just one for most of us.
Most of the ancient moral philosophers, as they pondered vices such as greed and acquisitiveness, were working with conceptions of use-value. That is, they could rightly see and condemn persons who acquired more things than they had use for. Such greed looked irrational, it was hoarding. Why would anyone want 1,000 chairs or shovels?
But things changed with the rise of money. Money shifted us away from use-value to exchange-value. Instead of acquiring chairs or forks--which have defined functions and, thus, inherent limits as to how many of these things are "enough"--we now acquire money which has no particular use or function beyond purchasing power. Money introduced liquidity into our lives, where goods can be reduced to money and that money used to purchase other goods. In modern economies liquidity is what makes the world go around. But liquidity makes is hard to determine how much is enough.
How much money is enough? It seems clear that a person with 1,000 forks has a bit of a fork-problem. How many forks do you really need? You only need as many as you have use for. But what about money? Does someone with with $1,000 have too many dollar bills? How about $10,000? Or $100,000? Or $1,000,000?
Because money has no use-value such questions seem odd. You can never have enough money because money is about exchange-value. Money can get you anything with a price, anything you need. Or want. And that's the root of the problem. When our desires shifted to money rather than to real goods and their function we lost our ability to draw a clear line between need and want and between necessities and luxuries.
Money, in sort, allows us to hoard. Someone with a million forks is clearly insane. But someone with a million dollars? To be sure we've tried to make a connection here. Misers are those who hoard money like a crazy person hoards forks. We think of someone like Ebenezer Scrooge here, a miser counting his money, hoarding it, having too much of it.
But the miser is an old-fashioned concept. The miser expressed a moral worry in the early years of capitalism when use-value began to give way to exchange-value. The miser was an attempt to apply notions of hoarding, a notion coherent in a world of use-value, to the new era of exchange-value. The miser was hoarding money. The miser had more than enough. Like a person with 1,000 forks.
But again, the miser as a moral concept has fallen on hard times. It would sound weird today to call a millionaire a miser, a hoarder of money.
But it's not just an issue with millionaires. Money has affected how all of us ask and answer the question "How much is enough?" We can never have enough money. And this drives greed, materialism, consumerism, and insatiability.
Basically, because of liquidity money hides our hoarding.
With the rise of money we've lost the ability to ask "What do I really need?" That's a good old-fashioned use-value question that we should spend more time contemplating. Unfortunately, our questions tend to be exchange-value questions, questions like "How much can I buy?"
And with those sorts of questions leading us forward the words of Paul seem particularly prophetic and apt:
1 Timothy 6.10
For the love of money is a root of all kinds of evil. Some people, eager for money, have wandered from the faith and pierced themselves with many griefs.