The cause was what exactly ?
It has been a few years since I flew the MD8x but I will have a stab.
For whatever reason be it WS or lack of visual references the crew elected to GA but neglected to push the GA button.
Scenario 1: A GA was initiated due windshear as was stated. - The procedure is.... You hit the button and pitch up. Holding the configuration i.e. Gear stays in position to mitigate ground contact and the flaps remain in landing position until warning ceases. However this is not how the aircraft was found... the gear was up and the flaps at GA setting. Which gives a little more weight to.....
Scenario 2: The A/c was at or below DA and a decision (by whoever/both) was made to GA due poor visual refs. The HP calls 'GA flap X' and thinks he hits the button. The FD's stay in LDG mode [LCZR] + [GS], the flaps travel up and the throttles also stay put as the a/c continues toward the ground. At Vref+5 with approach power set and GA flap travelling the A/c is not in a good configuration especially in gusty conditions. Sooner or later someone on the flight deck wakes up and notices this. A harsh pitch recovery from this configuration at low level in bad weather might easily have precipitated a departure from controlled flight, tipping a wingtip into the ground.
Windshear of not - There is strong evidence of mishandling close to the ground.