This is very sad. He looked like a great guy with a great family. Having lost my dad at 13, it ruined my life. I hope his children get a replacement father, but that is extremely difficult. I never got one and it ruined me.
Regarding the accident, I always want to know what not to do and what to do and thoughts for what to prevent. I'm not perfect and I always want to improve.
I have a speculation: the trees were cut before the accident, and he was missing the trees as road cue that the turn was there, and therefore failed to slow down or turn, trying to stay in what he thought was the roadway. This can happen easier with age or poor eyesight, driving by memory instead of sight. It could also happen more easily if distracted (see seatbelt speculations). Missing trees would be a bad deal in the dark for a driver like this (as I age, my eyes get worse and I use more memory cues than visual cues for driving, which is morbidly scary in San Jose with all the new invisible oddly shaped concrete medians). However, I'm not quite sure how this would cause him to stay so close to the crash point even at a light speed.
I found many other speculations here possible to.
I'm very surprised every time I pull over to do texting or phone calls and law enforcement pulls over and asks what I'm doing there. This has happened to me numerous times, and very often I don't see other people pull over to text or call. When I pull over, I find a safe and hopefully legal spot. This phenomenon of LEOs pulling over to ask what I'm doing was a few years ago before I started to see other people doing it a lot. Now days I actually do see other people doing it more often. This is a good thing. If driving conditions don't allow safe operating of some item (car settings, clothing, communications, audio controls, navigation, etc.), one should safely park first just to do it. I do this all the time. I consider my mental driving ability and visual information sufficiency to perform that function while driving, and often me being tired, mentally occupied, heavy traffic or poor visual contrast can easily make the difference between times when I consider it safe to do something en route and times when I have to pull over to do the same thing, such as taking off a shoe, or taking a look at my navigation map.