If they lay off employees, they have to pay severance and/or unemployment. If the employees quit due to unreasonable mandates, they can be fired with "cause".
If they can keep a bit of money for themselves by not doing this, they will not do this. For the people who run corporations the emphasis in "human resources" is on resources. You are to be mined for value until it is no longer profitable to use you.
Voluntary layoffs - probably the best form of layoffs if you ask me - still come with severance packages that have to be paid. Very few people will be interested in quitting just because you ask them, but a good many will do it if you sweeten the deal.
Basically we have 3 variants here:
Regular layoffs - have to pay severance + can select who leaves
RTO stealth layoffs - don't have to pay severance + can't select who leaves
Voluntary layoffs - have to pay severance + can't select who leaves
Any morally bankrupt business would of course want a fourth variant where they get to select who leaves and don't have to pay severance, but thankfully this option is generally not available to them.
Anyway, voluntary layoffs are the best out of a selection of bad choices for the workers, but come with the most downsides for the morally bankrupt business.