This voluntary layoff program is probably just the first phase of a broader restructuring. Look at the tech companies, Amazon just did this prior to their massive layoff this year. Companies start with voluntary exits to reduce headcount quietly, lower severance costs, (they save SOOO much $$$) and see which roles can naturally be eliminated before moving to any targeted involuntary cuts. Too sum it up if you choose to leave its MUCH cheaper and looks better for them.
This is also why your metrics seem to be unatainable. They move the goalposts and the employees they want to get rid of they hold them to the letter of the metrics and put them on performance plans to get them out or they just quit out of frustration.
Leadership at this company uses rolling layoffs as just part of their general business practices. VSP does a lot of things, avoid WARN Act triggers, and reduce the negative optics of “another layoff,” all while encouraging high tenured, expensive employees to self select out.
This looks like they still need to get rid of expensive administrative resources but want to do it in a controlled, lower risk way the keeps the public and legal exposure to a minimum. All at the same time giving them the talking point "we'll they left on their own".