In short: Capitalism.
It takes money (capital) to start or grow a business. The idea is that the business will make more money for you than you initially put into it. Most people do not have this initial capital lying around. So, they get a loan. Of course, the bank doesn't actually have cash for all the loans they give out, only a certain percentage, but they're large enough to absorb a few failed ventures.
So you get money, that didn't used to exist, for a business. The business makes you money, and you are able to pay back interest on the capital the bank gave you. So the size of the economy expands.
You have more buying power now. So you buy more. So value on goods goes up because there is more wealth in the system.
Other people expect raises because as they get more experienced because, the economy is inflating, and their time is becoming more valuable as they gain experience.
That last part maybe doesn't matter as much, because people are retiring, and younguns are entering the workforce for the first time. Except that people are retiring later and the population is expanding.
So, yeah. Capitalism essentially requires an expanding economy. If you wanted the economy to remain totally constant, you'd need a different economic system.
