Immigrants waiting for a Green Card must return to their home country to apply

This is how it works for legal immigrants for many countries.

That's how it works for legal immigrants, yes.

This seems like it could have some ramifications.

Let's saying you're dating somebody on a work visa, if you wanted to marry and sponsor their residency, would they now need to return to their home country to wait for the embassy?

The embassies reviewing applications put a LOT of weight on time spent in person, BUT they also require the US applicant to have domicile. So effectively, the only way to proceed is a long-distance marriage that could take years to process a visa for (remember: move abroad, and you could lose the domicile required to sponsor the green card).

So with our shrinking birthrates, our regularly documented & growing "will never marry" population, immigration effectively cut off, what does the future of this country even look like anymore?