Even though it's more than a decade that I flew the Fokker, I remember very well that the spinner of the engine was prone to ice up and cause vibrations, which could be stopped by reducing thrust. A modification was introduced by RollsRoyce, however, many carriers decided not to modify their fleets.
According to a friend of mine who is an ex-Fokker testpilot, preliminary information suggests that engine-vibrations due to ice caused the crew to reduce thrust. However, according to him, the engine is capable of shedding the ice by advancing thrust rapidly(one engine at a time of course). It seems that this was not attempted by the crew.
Facing an imminent crash-landing, trying to advance thrust even if it possibly destroyes the engines, seems to me good airmanship (remember Air Florida, where the pilots also never advanced thrust despite going down).
For the sake of the crew I hope my friends preliminary infos turn out to be incorrect.