Can only guess the reason for the Plat. $$ change at T-60 is mentioned in the FAQs about fees (bolding mine):
Why did you change the window from 21 days to 61 days for reduced fees?
A reduced fee is applied for members making changes to awards 61 or more days prior to original departure date instead of 21 days to encourage members to maintain their travel plans closer to departure. When a customer changes or cancels a ticket closer to departure date, it reduces the chance for that seat to be used by another customer.
SL