Because "you" didn't produce enough offspring to create a future workforce sufficient to pay for all of the benefits "you" expect to collect, so the government has to import a workforce to pay for it.
Bingo!
We stopped creating children to the point where it has stagnated the total fertility rate via contraception and abortion. Then we sent our manufacturing industries overseas.
If you stagnate the production of human beings you stagnate your economy.
What I keep finding out is that the creation of problems and their solutions on a national level start in the home.