It's an excellent way of getting your best people who have options to quit while the worst ones who don't are forced to stick around

Those "best people" may also be some of the higher paid - so if you only care about short term results that may be more of a feature than a bug.

Does Amazon do anything that requires best people anymore? They could probably survive on decidedly mediocre

Why would Amazon prefer that to layoffs or more aggressive performance standards?

Amazon not being on the hook for severance for a large percentage of high salary workers, plus not having them on payroll/benefits for the weeks/months it would take to transition them out via PIP (including the management overhead involved per staffer) usually adds up to just about enough in savings to go out and recruit fresh, RTO-willing, naive talent much sooner.

Amazon doesn't really pay severance for PIP, nor are they required to pay severance for layoff. They would be required to do a WARN notice, but how would that be worse than giving people 4 months of notice about the RTO policy?

Money, and being welcome at the country club.

Less liability.

Its not been my experience that changing expected work requirements causes you to have _less_ liability than layoffs.