Yes indeed, it's a cost issue. Typically when you want to fire people for financial reason you need to start talking with unions, explain them the situation, decide how many people you need to fire and how big the severance package should be.

On the other hand if an employee resigns, it's free.

For a time, big French corporations were known for their aggressive methods, putting employees in empty rooms with no computers and no work to do to "force" them to resign.