This is because of racial quotas (or per-country quotas) that exist for green cards. More here: https://www.forbes.com/sites/stuartanderson/2018/05/21/will-...
This quota should be removed.
This quota should be removed.
I think maximum percent limits make sense. But, 7% might be a bit aggressive.
After all, a country's borders aren't necessarily the best indicator of cultural diversity brought by those people. India (the biggest contributor to the H1B) is internally a lot more diverse than more ethnically homogeneous, yet highly populated countries such has Bangladesh, Russia, UK, Japan or France.
racial quotas (or per-country quotas)
Those are two very different things.