Because you get a runway to find a new job, you get a paycheck while you're on that runway, AND you get a severance at the end of the rainbow to tide you over i

Because you get a runway to find a new job, you get a paycheck while you're on that runway, AND you get a severance at the end of the rainbow to tide you over if you haven't found that new job (or a killer bump to the savings/nice vacation/whatever) if you HAVE found a new job by the end. In addition to your PTO payout, or whatever. Else if you flip your desk and walk out, you get your PTO and now you have no job.