My guess is that there was a struggle in the cockpit, but it was man verse machine. The aircraft was new and has an extremely sophisticated auto pilot. The planes can almost fly themselves. Normally, this is a good thing as it reduces pilot error.
But, poorly trained pilots are sometimes not fully informed about the auto pilot. As others mentioned, the airline has a history of safety issues which could include less than fully trained pilots. This possibility is increased by the fact that auto pilots are not always completely on or completely off. Rather, auto pilots can be partially on or partially off.
Then factor in the possibility of a partially on auto pilot leading to the pilots fighting each other while also fighting the auto pilot. In these cases, the pilots have only minutes to avoid a disaster by communicating effectively with each other, coordinating their efforts, then figuring out what is going on with the auto pilot.
Airlines train for these scenarios using simulators. But.... simulators are expensive to own or rent. Thus, some airlines are tempted to reduce simulator time.
