79 sensible answers already for the question. Let me throw some light from my point of view.
In order to dive from an airliner you would need to be,
in a stable altitude,
at low air speed,
and below about 12 000 ft (though skydiving is performed in 15000–18000 ft max).
One more thing is there won’t be enough time for us to prepare. For example, an analysis made from Air France 447 (Rio de Janeiro, Brazil to Paris) which crashed in 2009 took only 3 mins 22 secs from its peak altitude of the aircraft until impact with ocean. The flight is stalling and loses its control.
You’re panicking and trying to get your chute which itself loses a big amount of time and you need to jump from an opening, no other choice than a door. Someone should open the pressurized door and you cannot depressurize an aircraft over 12k feet since the passengers may pass out.
There is no way 90% of passengers gonna get their parachutes and be prepared in this short time.
There are several other reasons for not using parachutes in commercial jets,
The door of a passenger plane cannot be opened in mid-flight. Even military parachutists wait till the plane gets stable to exit.
Parachutes which can be used by an average person is big enough to slow down a whole airliner. This will be heavy enough, reducing payload as well as increasing the number of flights to transport the same amount of passengers.
Each parachute may weigh 8–10 kgs and too expensive.
It is extremely difficult