Because of a misconception that happiness comes by having outer comforts and objects.
But as we grow in wisdom we discover that some of the most important things such as love, peace, joy, strength, wisdom cannot be bought by money.
But even after discovering it people still do not know how to acquire these things. Hence, partly out of past habit, and partly in the absence of clarity about how to actually fulfill these needs they continue with the old ways of life that gives only temporary transient happiness.
Besides once addicted to the comforts that money may bring they end up as a slave to the pleasures it can buy. But soon, the pleasures stop giving even momentary happiness anymore and various forms of physical, emotional and other forms of suffering start catching up if one has neglected these areas. But by then it is too late to change unless one is blessed.
Affectionately,
Alok da.