There's significant paperwork and delays involved in switching one's H1B permit to the new employer. For that reason, the companies you can potentially move to are limited to those that have internal processes for handling H1B-based employment.
I’ve personally (and successfully) brought a H1B employee from a BigCo into my 15 person startup (we were actually 7 people at the time of hiring them).
There’s some paperwork, but it’s not a major hurdle. Maybe a few grand in legal fees and a few hours of work on the employer side.
and your personal experience shows what?
just go to any job anncouncment website and see how many specifically say that Visa Support is not available (thus requiring US Residence) and how many say it is.
the Ratio from a glance is maybe 1/100 has a Visa Program.
It also depends on where they are in H1B process. These days perm and i140 approvals are taking ages(2 years). Basically engineer is stuck while they come out at the other side.
Also a lot of employers who had layoffs aren't sponsoring new Green cards because u know...