Fuel starvation is a likely cause
It's possible the guages weren't accurate. It's possible the fuel consumption was higher than expected or that less fuel was loaded than the crew believed. It's possible there was some form of fuel line blockage. It's also possible the crew was distracted by the landing gear malfunction and ran out of fuel. It wouldn't be the first time a crew has done that, even highly experienced airline crews. A 4-engined plane just doesn't normally lose power to all engines unless fuel starvation took place.