Yes but the GP used poor individual performance as their only positive reason of layoffs not needing justification. So the reply was that individual performance is almost never a factor in actual layoffs, a point which you and I agree with. Thus, poor employee performance is not a monolith that can be used to explain all layoffs, and these companies should have to give better reasons that align with actual reality.

It's about the immense asymmetry of power here. Yes, a person can leave just like a company can fire. But a single person quitting is nearly never a massive disruption to the business, but the business firing someone is nearly always a catastrophy for that person.

I don't need to justify quitting because I'm not harming you by doing so. Laying off hundreds of people absolutely requires careful and validated justification as your significantly harming nearly everyone impacted.

Of course these companies do pay well usually, but not all of them do, and not every individual has the privilege of cheap health and rent and a cheap family. Any single significant factor in a persons life can cause that "well paid" factor to mean a lot less, especially if it drags out to 6 months or more like it is known to do