Because that is not how American immigration has traditionally worked. Many of us are from families that did not have the means to put someone through graduate school, they arrived as Irish orphans or with $8 in their pockets. The graduate student doesn't need the citizenship, the person with $8 in their pocket does. Imagine a world where the graduate student who is already guaranteed to be pretty successful AND the immigrant who came with $8 dollars have good lives. That's what America is about to me. That is why we limit immigration number by country (so more people have an opportunity) and promote familial immigration, not immigration of elites. If you want that system there are plenty of countries with golden visas, one right next door to the USA.