Operator error usually under an open parachute with Aircraft pilots calling such incidents mid-air collisions or controlled flight into terrain.
Out of 12 2011 North American recreational skydiving fatalities
5 skydivers died when two jumpers under open parachutes hit each other
3 died landing under open parachutes
2 no pulls (one with an automatic activation device that didn't leave time for the reserve to open with the root cause potentially a medical problem, one without)
1 cutaway too low from a malfunctioning parachute
1 skydiver left his harness (possibly a suicide)
Out of 21 2010 North American recreational skydiving fatalities
5 low turns into the ground
5 canopy collisions (one unable to deploy his reserve after the wrap)
3 no pulls
2 canopy collapse in turbulence
1 wrap in a canopy formation
1 collision under canopy with electrical cables
1 low cutaway from a malfunction
1 hard landing in high winds
1 low reserve opening followed by a hard landing (probably a medical problem)
1 suicide
Skydiving can be dangerous if the equipment fails or the pilot makes an error. For example, hard landings, failure of the main and reserve parachute (extremely rare), canopy collision, freefall collision. With training it is possible to eradicate the likely hood of having a problem and thus the question of 'why is skydiving dangerous' becomes 'is skydiving dangerous to everyone who takes part'.
the most cause of vehicle accidents is when you text while you drive
Statistically, driver inattention is the most prevalent cause of most accidents.
The most common cause of transportation accidents is the driver being sleepy. The second most common cause of transportation accidents is the driver driving under the influence of alcohol.
The most common cause of motor vehicle accidents is driver behavior. Most can be blamed on excessive speed or aggressive behaviors such as tailgating. Driver distraction is also a cause of accidents.
Human Error
Traffic
The most common cause of snowmobile accidents is that the rider loses control of the snowmobile. They go too fast which results in loss of control.
most likely running rich, too much fuel
Car accidents
the inability to swim
Most car accidents happen because people are careless. People also do things while they are driving that cause accidents, such as using cell phones, texting and eating.
drink drivin' is the most common cause.