Regarding little or no fire, the engines, as the heaviest,
must have been thrown far forward by the cartwheeling fuselage,
away from wings full of fuel.
Also most of the fuel might have been already spilled after the wings
hit the trees 1 km before final impact.
Just my guess.
You don't need running engines to ignite a fire in a crash impact. There are lots of sparks from just metal friction.
Key element is fuel atomization.
Wet ground reduces the chance of a fire but does not eliminate it.