The problem is the 1500 hours is an absolute minimum as we know. You can only unfreeze an ATPL during your instrument revalidation (LPC) which only comes around once a year. If your LPC falls when you have 1501hrs and you meet the requisite requirements then great, if you're on 1499 hours or less when your LPC is due then you'll have to wait another twelve months to your next LPC and dependant on how many hours you fly in a year you might be on somewhere near 2300 hours. I can't imagine that many pilots unfreeze right on or near the 1500 hour mark, in which case by the time you do get to unfreeze it most pilots will have achieved the requisite criteria.