The harder it is to change jobs or explore opportunities in parallel, the less employers have to compete.

There was a whole lawsuit about no-poach where a group of employers chose explicitly not to compete by agreeing to not hire each other's employees. I believe the same effect can be had by simply adding friction to the structure of the market itself.

What's amusing to me is the brilliance of it. It essentially exploits egos in the workforce to suppress their own wages.