Hmm, this is a tough one.

Just playing devil's advocate here, but even if you know that you can walk all the way back to "somewhere", you could also be making the situation more difficult for other people.

Drivers who abandon their cars make it harder to clear the road and reopen it to traffic, and major freeway like I-5 will be a priority. Reports of people hopping the guardrail and hoofing it cross-country could waste valuable resources on SAR teams sent to make sure those people are all right or to give them a lift because they're too tired or dehydrated to go on. Even walking back along the freeway, at some point, you may encounter free flowing traffic again, and people walking on the shoulder of an interstate is not a very safe mix.

Yeah, it's a tough call. What seems common sense to you as an individual may just cause bigger headaches to the folks trying hard to help all of you stuck in the same situation. It's like people stuck on a jet plane on the tarmac in winter. "Obviously" turning the plane around or bringing those movable stairs to the plane so you can walk back to the terminal seem like common sense solutions, but people don't realize the difficulties involved that prevent such "common sense" actions from taking place.

I certainly don't have a ready answer for this since there are so many variables involved.