Usually some form of mis-management which in this case may have put pressure on the pilot to accept a shorter take-off option due to some minutes of time saved. Sometimes pilots also might get their priorities wrong. There's a concept of "get-there-itis" which is also a common cause of crashes but it's currently unclear if it was a factor in this case.

I imagine in a while we will all be able to read the investigation reports, since the aircraft crashed shortly after take-off the black box recorder should contain all the information we need to figure out most of what happened including possibly the reasoning for the decision to make an intersection takeoff.