I don't think enough information has been released for me to have any ideas on what really happened. That said, a hit and run on a clear day with as much traffic (a car every couple minutes sometimes more), or animal attack is not what I think happened. (Mountain lions avoid humans and attacks are extremely rare and that would have left clues, not to mention drag marks, etc).
Getting lost for that particular place is hard to believe as well, as there is a non-motorized trail which they presumably hiked, and Kelbaker road is visible, and audible. Also, very few hikers hike off trail, those who do would not be wanting to wear shorts, as the area is filled with various cholla cacti, which have hooks that get into your legs, very unpleasant to get stuck by those! Even the I-40 is visible and a turnout at the pass is visible by eye. Less than a mile west of the road which runs north/south you have Granite Mountain, which is a sheer wall of rocks, she wouldn't have walked that way, unless extremely disoriented. They don't sound like rock climbers, so that's highly unlikely.
I'm hoping the husband will offer much more specifics about the hike and time than he did in those two short interviews. Some mention all they had was a beer, another article mentions they brought a gallon of water as well. That small detail makes a big difference in how far you can hike. A beer in hand, and your hike during mid-day is limited to no more than a mile or two, but a gallon of water, and now you'd have to expand the possible range to search by a few more miles.
Having hiked at this location my main observation was just how many places there are there to shelter from the intense sun, which of course also makes the search harder and makes it harder for aerial photography to pick up any clues. The scattered boulders south of the main rock formations also had lots of nooks and crannies to hide. I noticed SARS had tags going for about a mile south, so it looks like they covered that area as well.
If I were in trouble with the heat I might be tempted to go under a large boulder and wait to feel better, these are great sheltering places, but that is not what Robert Thomas suggested. He implied they had already gone to the rocks and were on their way back, between the main rock formations and the trailer there are no rock formations to hide. If she had gone for the closest boulder formations, she would have been found though, because they searched those formations extensively, see attached photo for an example.
It is uphill to the boulder formations from the trailer location and only .5 miles away, downhill back to the trailer, so getting back would have made more sense for me if I thought I was in heat trouble. But RT did not mention his wife had issues with the heat during that hike.
I'll attach a few more pics so you can see landscape and trailer location in relation to the surrounding landscape. Last photo shows the wall of rocks on the western side and a orange tag showing they searched to that extend.