It was inevitable as soon as enough people believed that spending money is necessary to live. Money is the next stage of life. As individuals, people's only truly limited resource is their attention, their time, and so the same is true of Humanity as a singular whole. Money is a way to coerce another person's attention toward an endeavor that benefits the spender, like paying the chain of farmers/pickers/processors/distributors to grow and ship my food to me instead of having to do it all myself. And so people say Time = Money.
As a commutative operation, then, also Money = Time. Humanity and Money are both driven to create more of themselves, but as long as the growth of money is allowed to outpace the growth of Humanity, money will become the dominant life-form once there is more of it than there are humans to be the Time-unit. The only thing keeping it from happening before now was the lack of an instantaneous global means to transact.