No one will know why Mr.Kim decided to take that road, as unwise as it was. He had missed his turn off to Gold Beach and this was the next available road to take him there. Not being from the area he probably had know idea how bad it really is. From my understanding the road is very narrow and has turn offs here and there for turning around or letting other cars by. Whatever the case he probably figured he had gone that far so why turn around, plus, from what I hear, he may have been getting low on gas.
Here's my other take on it. He was driving a Saab. I jokingly call them Saab Snobs but the reason I bring this up is this. Saabs, like Volvos and Subarus are known for their agility on snow. Many models have AWD which really helps in snowy conditions. The side affect however is overconfidence by the driver. I don't know how many times I've been driving up to Mt.Hood in my van in horrible conditions and seen some A-hole idiot in a Subaru or Saab scream by me as if their car was glued to the road. The same overconfidence is exhibited by some SUV and 4x4 drivers. This may have played a part in why Mr.Kim felt he could take this treacherous road in the middle of winter.
Also, the photo of where he started and where he ended up is a little decieving. He traveled five+ miles but he only ended up 1 mile from his car (as the crow flies)