I spent several years of my working life investigating motor accidents for an insurance company, taking statements from drivers and witnesses, visiting scenes, taking photos and measurements, studying police reports, negotiating with solicitors, occasionally attending court.
Most road accidents are depressingly banal: a moment's inattention, or overconfidence, or panic, occasionally exacerbated by alcohol or drugs, and sometimes by poor maintenance of the vehicle. It is easy to overthink what happened. People make mistakes and accidents happen.
However, I agree with
@Cochise that it is inappropriate to speculate about the cause of this particular accident on the basis of a few lines of news report and a few seconds of video which start from after the vehicle was already out of control. There are no clues as to why the vehicle was travelling at that particular speed, in that direction at that moment. “It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts.” (from A Scandal in Bohemia)
A friend of mine in apparently good health set off to the local village to buy a newspaper, had a heart attack at the wheel and was probably dead before his vehicle had veered off the road. Things happen.