Because resources are finite, and already divided amongst older generations. It's a basic flaw in economy that the older folks don't want to talk about.
Would you agree that civilization has more resources today than 50 years ago, 500 years ago, 5000 years ago?
We transform raw materials and come up with ideas and combine things in new ways that are more than what earth provides.
We create wealth.
You're right though that there is a basic flaw in the economy that older folks don't want to talk about.