I've managed a team at one of the big tech companies for a bunch of years. I've managed a couple people on h1b, all with graduate degrees from premier US institutions.
Never once have I heard anything even resembling "work your h1bs harder because they won't leave." They all joined on the same pay scale as legal permanent residents and were all evaluated through a process where nobody else in the room knew who was a legal permanent resident or not (I only knew because I needed to sign off on forms describing their job responsibilities to the government).
At most this is some aggregate effect of "people changing employers less is good for employers generally."
This doesn't really vibe as abuse of the program to me. I'd vastly prefer it if the policies gave people on h1bs significantly more confidence in changing roles and more time to find a new job should they lose their job, but is this really a decision of the tech companies rather than an output of the immigration policies?