>if you make more than a certain amount not if you invest over a certain amount.
I don't know any developed countries with that system. Do you?
There might have technically been other minimal requirements like knowing English or the local language, but most people who fulfill the pay requirements will fulfill the minor requirements too if applicable.
If so that's not the same as an income requirement at all.
If not, I'd like a list of them because that's very interesting.