The question is how hard did he try to stop? If you have skid marks, it’s remarkable that the vehicle stayed upright and straight; and if it was trying to stop full blas, stand-on-brakes, you’d think that detail would make it into the eyewitness acounts… although “he didn’t even try to stop” sounds more dramatic on tv news.
This is the point; a 300-footskid instantly contradicts eyewitness testimoy if they all really said “he didn’t TRY”; giving you a good idea of the challenges ahead for the NTSB and the level of detail they have to dig into.
As mentioned above, EVERY possibility has to be dug into and ruled out. That MIGHT take a year or longer - reported on the TV news with the same dramatic flair “the investigation will take a year”.