Yes, now you're acting as if I didn't just say the same thing. They arrived on a Friday night, it was not possible to search everywhere. They never search everywhere. No one has every searched the entire Mojave for anyone.
However, they do have methods for establishing an early (short) perimeter, based on averages. They also had some daylight. I think they did have a helicopter out but not for very long as it got dark.
For 9 days, they tweeted their search parameters (and did check some other nearby intersections, which is obvious why if you look at the aerial map of where RT says he last saw her). They widened it. They walked in brush that no normal hiker in a bikini would walk, as it was filled with cholla. Cholla look really nice, they are really nasty, even the non-jumping kind. And they even tweeted about that (at least some of the SAR team did). They could not look under every cholla (but what living person would be there?)
Later though, when it became an apparent body recovery, they did re-search the area and posted pictures of them, and their dogs, poking around under the cholla. Beating the bush, as it were. And of course, they had widened the radius of the search every day that they searched.
The first priority was to search trailside (there are many trails) and in obvious places, in search of a live person. The early perimeter (afternoon one) looks to be about 1.5-2.0 miles in each direction from where RT last saw her (which is why his information was crucial) and then, by next day, including 1.5-2.0 miles from where they were parked (on foot) and way bigger radius for the helicopter(s). I can't recall now if it is was one or two.
The first day, they confined themselves to grid squares located off the main trails (obviously). They walked close together and marked off their grids with flags (couldn't use string out there). Some areas were not closely examined by eye that first night (cholla thickets). Anyone going into a cholla thicket alive would start screaming.
They had no reason to believe Barbara had been out of sight of her husband for more than 10-15 minutes, that she was sane and sound when she walked less than half a mile to the RV, etc. I'm sure that as this search evolved, so did the view that RT needed to say more.