I’ve been on H1-B briefly. The suggestion that anybody on H1-B is on a high tax bracket is false. I know people with 60k salary on H1-B.
There are also 2 groups: one are the international students with advanced degrees, but companies can sponsor employees from abroad without any advanced degrees from US universities. About 72% of H1-B visas are issued to one single country (India). A lot of them are hired by tech companies for cost reduction purposes since an employee from India will likely work on a lower salary.