Jetblue has always sold PTO to the pilot group as a method to make extra money by selling it back. It has always told the pilots this time is for your vacation or personal use. With the inception of the dependability policy PTO is no longer for use at your discretion. The airline is notoriously understaffed which makes using PTO to drop a trip nearly impossible. Should you decide to call in sick you are now subjected to a dependability policy review at the discretion of your chief pilot which can lead to discipline.
You will notice that the vacation period allotments are incredibly scarce in months other that trough periods. This is a major complaint amongst pilots because most cannot get a holiday week or summer vacation week unless their seniority resides in the top 20%.
In short, PTO is for personal use provided usage falls within a period of time designated by Jetblue which doesn't interfere with IROP's, holidays, summer months or peak flying periods.

Sick time at a major airline becomes a fiscal responsibility year over year for the airline. PTO and its expiration or limited accumulation is Jetblues method of circumventing this industry standard benefit.