In 35 years of IFR flying, I have never been forced by ATC to land at an airport that I did not request to land at. The only scenario that I could see that happening was during 9/11, where they forced everyone to land ASAP.
Likely the pilot thought he’d be able to do this flight VFR, and got himself into a bad situation without enough time to get out of it. Given a choice between going IFR or crashing, I’m sure he would have climbed and gotten an IFR clearance. Sometimes people lose situational awareness, and if you’re flying close to terrain with low visibility, there isn’t much room for error. Hindsight is 20/20.