You arrived at this range of numbers how, exactly? Your what "it needs to be" needs to be revised because it isn't happening.
You're wrong for two important reasons. The first was pointed out already: people's incomes can grow. The population can decline by 20% and incomes rise by 200%. Governments can spend on any number of things: defense, welfare, infrastructure, industrial subsidies, research, etc. Economies are always supply constrained, you can only consume what's been produced.
Yes, people will only ever need so many washing machines, but you can make things other than washing machines. Needing more people so they can make and buy more washing machines is how you get stuck in the middle income trap.
The second and more subtle reason is that some economic activity doesn't have a source of final demand. There are closed loops in the economy, especially the industrial economy, and they're very important. For example, you mine iron to make excavators to mine more iron. Another more pertinent loop is making chips to put in computers to write EDA software to make more chips. There's no "final consumer" in any of these loops, every consumer is a producer for another node and vice versa.