Genuine question from a non-aviator, having just landed safely at 150kts or whatever the speed was, why is it deemed unsafe to slowly taxi the aircraft far enough clear of the runway so the airport can remain open?
Fair question...
The answer can vary and we do not know the exact circumstances here. But as the TV showed, the runway filled with emergency vehicles. So priority 1 is to stop the aircraft on the runway and get it assessed ASAP, and a narrow taxiway offers less options, and takes longer.
If the aircraft is assessed 100% safe, and can be taxied, then you might choose to do so. However, without full gear, probably hydraulic problems from posts above, I would guess it was never an option here. Just look at how close the #3 engine was to the ground.
There is a theme running here... safety is priority #1. Airport running efficiency very much #2. Also the case with NATS - despite all the fuss over the Dec 2013 and Dec 2014 computer problems, there were nil safety issues. Does not stop the MPs going off on one about the delays of course
