There's a big difference between requiring a minimum wage for anyone and specifically requiring a higher wage for existing H1-Bs. In particular, the fact that H1-Bs will have to emigrate if it isn't increased.
The H1B can be and does get renewed by 100s of thousands of people. AC21 provision allows for an H1B to be renewed in perpetuity (even beyond 6 years) until an approved green card petition is pending. The approved green card petition can stay pending for a really long time due to country based immigration queues which disadvantage people from large population countries.
H1-B is a dual intent work visa an you're not required to emigrate. You shave the option to extend your work permit for 6 years or pursue permanent residency.