I would say it is because of a couple of reasons.
That is what you are taught in life while growing up.
Brainwashing via television that more is better. Bigger is better.
It is driven into people that money can buy so many things. (But not happiness.)
Many souls are younger souls thinking that money is of value. Rather than happiness.
In growing up it is inherent that you do not want for someone else to have more than you. So there is a strong striving to have more money so you can beat everyone else out.
All of the real important things like happiness I missed by the majority of people.
Money is mistaken for happiness. Money gives comforts to some degree and is often there is a temporary happiness. As it is said, “You can’t buy happiness.”
Best Regards
Gaurav