they might have had to wait for the brakes to cool after a max weight, high speed reject.
Nah, that's why the French fitted hair dryers to the wheels!
Oddly enough I was behind a Caribbean Airways flight departing from Heathrow 27R a few years back before they changed the taxiways in that corner and he drove onto the grass and got firmly stuck! Caused equal amounts of chaos there as well.
Personally I find JFK is a mess and this sort of incident is always an issue. Kudos to the Jet Blue guys who reacted pretty well IMHO.