No comment on the initial decision to fly this a/c at an unfamiliar altitude/regime.
As a past instructor on the 604, very similar to the RJ's systems, I have observed many difficulties in the operation of the (very simple) bleed air system - the correct selection of the (4) switch-lights would be essential for the success of an APU start of the first engine, and if attempting a relight at below 13000 with the incorrect bleed settings, a mundane selection of one switchlight would have precluded any attempt at a relight and the ground would seem very close at that point.
This situation would see the crew attempting to function in a very noisy and very non-standard environment:
The ADG would have been deployed - noisy, vibrates tremendously, and very distracting
I think the autopilot disconnects on an RJ with power loss? It does not on a 604. Somebody needs to hand-fly?
Reading the QRH with a flashlight?
There would have been a stack of messages on the EICAS with the associated chimes and flashing Cautions/Warnings
Getting the APU started?
ATC?
O2 masks? If so, difficult communications between crew with loud Darth Vader noises (that's a second area where finger-trouble is common)
Navigating? Where the hell is that airport? Is someone attempting to program the FMS and operate the QRH?
Will the APU start?
F/O overload? Probably.
Stress level off the scale - a long time to contemplate the end.
The wreckage was inverted - another stall? Probably they were very unfamiliar with hand-flying, and following the correct (seemingly too-fast) airspeed means giving up a lot of altitude.
Once these guys lost the two engines, and recovering from the initial stall, doing the rest correctly and in a timely fashion would be stressful enough in the sim, let alone in the real a/c, and you must be trained to make the right decisions when it all happens. E.G: do you driftdown initially to evaluate? If you decide to do this, planning eventually to start the APU, you initially decrease your airspeed to about 210 knots for very leisurely descent. This low speed would probably cause the N2 cores to "lock;" returning to windmill speed would require giving up a LOT of altitude, and the engines are 6.2:1 ratio so you would get a very lackadaisical response from the N2...you would have to hold that dive for a long time.
As your altitude decreased you would also have to decrease your driftdown (=VFTO?) and this would also always be the slowest speed you fly at...another page in the QRH.
Or do you immediately point the nose at the ground, right after stall recovery, effectively diving the a/c to get the cores to spin, and decreasing the time you have to "manage" this "event?"
A bad one, gentlemen, rife with speculation for sure, but I have seen this screwed up in the sim in a 604, so I can see the pitfalls.