I think it's exceptionally unlikely that companies are doing layoffs instead of firing for the benefit of employees. You're holding up reasons like severance and saving face.

From everything I've seen, the much more common reason is that firing someone typically entails a much longer paper trail for CYA reasons. Batching them up and including them in the next round of layoffs is easier and safer.

Severance packages always requires signing a “I give up my right to sue you” document. It is 100% about lawsuit reduction and 0% about being gentle with employees.