The inquest as to what caused the failure is still ongoing and may not be resolved for the better part of a year. But officials believe that, specifically, Schiaparelli's inertial measurement unit was oversaturated for a second, which told the system that it was already below ground. As a consequence, the lander fired its parachute, ejected its heat shield and fired its braking thrusters all at once while still 2.3 miles above the surface.
It's the second time that Europe has attempted to land a vessel on Mars, only for something to go wrong at the last minute. Beagle 2, from 2003, which successfully arrived on the red planet, but failed to deploy its solar panels to power transmissions. In fact, the craft was only found in 2015, when a NASA spacecraft shot detailed images of the proposed landing site.
Europe's space bods aren't too worried about the failure of Schiaparelli, and will continue to work on the ExoMars program. It's hoped that the next mission in the series will launch in 2020, hopefully with a computer that double-checks its math during a landing procedure.