Why is it that even within the EU we could more than half immigration tomorrow, as the majority are from outside the EU, but no government will?

Why is it that all rich countries are actively encouraging immigration?

https://www.newscientist.com/article...ed-immigrants/

We are getting old as a nation, and we need working age people to pay for us.
Even better if they stay for a few years and then go home before they are old.

I don't think immigration could be any different outside of the EU.