I was on another flight at the same time which experienced a similar issue. Weather moved in quickly in the afternoon and blocked all departures to the West. There wasn't enough fuel to fly around the weather and make it to the destination. Weather moved in and out over the next several hours and long takeoff delays accumulated. Eventually, we neared the 3-hour tarmac delay limit and the pilot was forced to return to gate. The pilot then timed out while at the gate, and the FAs timed out while looking for a new pilot.
Because the same thing happened to multiple DL flights at JFK, no surprise that it took a long time to find new crews to staff all of the flights.