Regarding your last sentence, what you say does makes sense, but it is important not rule out the ranch property itself, just not to miss an easy option (which sometimes killers do, despite the obvious dangers in that choice).
BTW, I think the Simpson ranch might be the first area the LE searched for Suzanne in that county, since I'm certain they obtained a search warrant for it.
A second reason to search near this ranch is because BS is familiar with that area. So, not necessarily at the ranch, but near the ranch, say within a handful of miles of the ranch.
A third reason to search near this ranch is because BS was observed, in the affidavit, to have traveled in his black truck mostly along a path from Boerne, TX, then using TX-46 and TX-16 to Medina, TX. And that path takes him right past the ranch on Highland Dr, which is just north of TX-16. So, if he knows of hiding spots on/near the ranch, then it is very tempting for him to use one of those spots, since he is traveling right by there anyway.
A fourth reason to search near this ranch is that, according to the affidavit, the ranch is the near the point he stopped traveling mostly west, and he started traveling mostly east. (Specifically, that point was in Medina, TX, which is just 10-min drive from the ranch.) Again, by "near the ranch", I mean it could be within a handful of miles of the ranch.
A fifth reason to search near the ranch is because it gives BS a good excuse for why his truck was parked there for 1 to 2 hours, since otherwise his truck might be noticed as out of place. Here, please consider the idea that he may have dropped off all the supplies (large bulky item wrapped and secured in the blue tarp, 1 bag if Quikrete, 1 jug of water, orange HD bucket, and possibly other things) parked the truck somewhere that was better hidden (or at the ranch) and walked back to that drop-off location to do the disposal work. So, again, just because BS was somewhat near the ranch (or another stop near TX-16) does not mean he had to do the burial on the ranch or just off the road. Instead, in 3 trips (1 for blue tarp, 1 for a bag of concrete, and 1 for everything else), he could carry everything up to 0.25 miles or even more. That approach would be strategic, since police know from many cases that bodies are often are NOT moved more than 0.25 miles from a drop-off point, because of all the work and danger involved in that, and police searchers often don't look beyond that distance, unless they have a very good reason to do so.