1) Snow, obviously. Some gates were closed as snow was removed
2) Slowed ops. Everything moves slower in this bitter cold
3) Diversion recovery. Many of aircraft flew back to JFK on top of a normal schedule. Can't handle that volume
4) General incompetence. Terminals at @JFKairport are independent fiefdoms. A T1 airline can't use any other terminal. They must wait for T1.
5) @JFKairport doesn't care. "It's not my problem" is a main theme there. This is an airline/terminal issue, not airport issue.