Its good to remember - Its not that it was impossible to get off, its that someone decided not to drive a stairs over to the plane. ALL airports have portable stair units for passengers to walk down and into the building. They decided not to use them.
The article indicates that the airport was struggling with lots of snow and power outages:
After landing, the planes reportedly sat on the tarmac for up to seven hours as snow piled up around them and the airport struggled with intermittent power outages, according to JetBlue.
If that article is nearly anywhere close to accurate you would need to use one snow cleaning machine to prepare the route for the portable stairs (which typically are motorized, and will get stuck in snow). Probably you'd also want to use a shuttle bus to ferry them from the stairs. You don't send 200 frustrated airline passengers walking for perhaps half a mile in a blizzard.
I'm speculating here, but I would guess that the airline company has absolutely no authority over the snow cleaning equipment. Which would be busy trying to keep the runway and taxiways clear, not really bothering about some plane parked in some airplane parking lot.
I would also guess that anyone capable of commanding the combined use of stairs and snow cleaning equipment would be totally overwhelmed with the calamity of the situation.
EDIT: I can't imagine those in charge of an airport saying "NO" to a clearly stated request for a quick assistance to relieve 200 passengers from more hours in discomfort (such as using one snow truck for 10 minutes). That request was probably never made.
Making that kind of requests requires that you A) think a little creative beyond protocol, B) takes initiative, and C) know who you should ask.
And all 22 gates busy for every minute of the 7 hour delay...hard to imagine.
Also, those 22 gates could very well be occupied for the whole time by planes that were waiting for the situation to improve before going anywhere.