To me this looks like something that could be explained by a medical incident. They were on track before a sudden hard left deviation. Also supporting that is the crash came right after the ATC controller advised they were too low for flight following, however, that ATC controller had asked a question seconds earlier that went unanswered by the pilot. After several seconds of no answer he just goes ahead and tells him that he can't get following. So there is some reason a previously quickly responding pilot did not respond to the last questions asked. Either work overload or medical problem.