Apparently fires are not that easy to start in real life. There was a jabiru in Bundaberg in which smoke came out of the engine compartment. The plane subsequently burnt on the ground back to ( but NOT including the half-full fuel tank ). There have been a couple of others lately, like the plane in the power-lines, where there was no fire.
I have only been around one crash in my 50 years of flying, and that was a Sonerai which DID catch fire. But a guy I knew well crawled out, covered in fuel, through the broken windscreen of a Cessna in a vineyard. Luckily for him there was no fire.
Just recently, a pub in a nearby town was shattered by a car and there was no fire. I reckon it was lucky that they didn't deliberately light a fire to get rid of any forensic stuff.
So.... movies would have you believe that a fire is the usual thing, while my experience is that it is unusual unless deliberately lit.