I'm pretty convinced you don't have solid understanding about inner workings of immigration and H1-B. You just have some hatred against this visa.
Most of jobs holded by h1-b candidates are temporary and their ranks stand at the very bottom of the food chain. These jobs last not more than few months and in very rare cases 1-2 years. So, they are the first ones to leave the company before the permanent ones.
H1-b candidates are very expensive to hire. Although, they do get paid very low.
Now, please go and educate five other people so that we can end this BS propaganda.