system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why is a decreasing population considered a bad thing for a country?

Why is a decreasing population seen as a negative for industrialized countries? Doesn't increasing automation technology mean that with less people everyone will have more? Surely cities being less crowded with higher average wealth is a positive?

What am I missing?
gpt
People are an input into the economy, just like oil or farm land or machines.  As a general rule, the more people you have, the more you can produce. So, on a surface level, a shrinking population is bad for an economy in the same way that a dwindling oil supply or lack of capital is bad.

Unlike most of those things, people also create demand, not just supply. So fewer people can also mean that people aren't out there looking to buy new stuff---especially land and houses. which can also upset the economy quite a bit. 

On top of that, shrinking populations also usually mean aging populations.  As people get older they tend to go from being net producers to net consumers, especially when health deteriorates.  This can force a country to make hard choices about how, and how much, to support an older population that increasingly can't support itself.  This is made worse by the fact that some jobs simply aren't suited to older people (There are very few 80 year old coal miners, or 70 year old ER nurses, and even when people are only 40 or so they may find that family and health makes it hard to work the kind of job or hours they could have worked when they were 50.)