Higher speeds consume more fuel than lower speeds and MUCH higher speeds consume MUCH more fuel.
It SEEMS that maybe the pilot was in a rush to go somewhere and he burned much more fuel than he thought he would and therefore ran out of fuel and crashed.
The problem is that the new search area is the same area that actually assumed a slower air speed — 400 knots rather than 450 knots:
https://www.facebook.com/178566888854999/photos/pcb.740971779281171/740971732614509/?type=1&theater
and they don’t know how much fuel he had, or burned, or had left when the plane went down.