It is so they can have more leverage over them. A person on an H1B visa is basically guaranteed labor who will have to accept anything their employer throws at them, because they have no realistic options to leave the company until they get their green card.
Intel deliberately tailors their preferred qualifications (PhD RCGs with no work experience, and probably 90% of people in that category are international students) for engineering roles so that they "have to" hire nearly exclusively H1Bs.
It is very predatory and messed up.