Occam's Razor says: or the companies just want to rehire new people at lower pay.
And what you say simply isn't true anyway - I even studied EE, but all my professional experience is on the web, I would have a long ramp up to be productive on an embedded team. I probably shouldn't even be hired for a grad position on such a team, a fresh graduate would have better memory of domain-specific stuff.
What Occam's razor actually says is that in the face of multiple possible explanations, the simpler one is the more likely one. Your suggested explanation seems a more complicated conspiracy than simply not needing/being able to afford people to me.
Do you have any idea how much it costs to recruit replacement developers? Between the cost for recruiters, the amount of time spent on interviews, and ramp-up time for new hires, you'd need to lower wages by a significant amount (eg. 30%) for you to be able to get payback in a reasonable amount of time. Not to mention, if you're a startup, the loss of institutional knowledge will greatly hamper your ability to execute.
Given that redundancy is a more complicated legal process it’s unlikely you’d use it for this purpose.
This was widely considered to be fire and rehire, although the government position was that it was “just fire”. So companies are willing to skirt the intention of the law.
