I think it is more about the employees who stay. Giving unlimited PTO is a way to make the remaining employees more happy. So it is like a way to try to balance out the negative effects of the layoff on team moral...
There is no contract stating how much PTO you can take, its up to your manager, could be zero, could be four weeks, who knows. Could change when your manager changes.
Its an accounting trick to remove PTO from the accounting books and remove a paid benefit to employees.