In current US immigration policy, a green card holder's spouse must wait outside US until his/her immigration case got approved.
Such cases for people from China or India will take on average four or five years. Suppose a person just get his/her green card in the first year, and subsequently he/she get married with someone back in his/her home country. Then his/her spouse has no proper visa to enter into the US to stay with her husband or his wife unless the immigration case approved.
F1's spouse has F2 visa, H1B's spouse has H4 bisa, J1's spouse has J2 visa. Why the government cannot create another visa category for green card holders?
No matter what the excuses are, legally seperate husband and wife for more than 4 years is not a humane behavior.