Looking back through my logbook, the most common cause of diversion has been medical followed by airspace closures. I can’t remember the last time I had to go somewhere else through lack of fuel at destination and I rarely take any extra.
Thats very interesting. Do you fly long haul? I ask because in the last 20 years of passenger flying I have never diverted due to medical or airspace but have diverted many times due to weather. I imagine the length of the flight impacts the likelihood of medical diversions and the part of the world influences the weather related diversions.