Well, firstly, it's erroneous to assume they intentionally went on a rugged expedition unprepared. Joshua is beautiful, heavily traveled riddled with little super cool things to see. Unfortunately many of the super cool things to see that you hear about are not well marked and easily traveled paved walkways like the dozens of maintained heavily traveled sites.
JTree in heat and sun is surprisingly difficult to see in. It's not just bright, but the car above is a good example, that car will be hard to see until you're on top of it. Look beyond the car and what you see is a large plain littered with J-Trees, rocks, actually isn't flat and basically same-ness in all directions.
It is super easy to get lost, turned around and disoriented. Even more so on any kind of poorly marked primitive trail going to a lessor known site. I've been on them and the primitive markers basically maintained by other hikers are often only visible going in one direction.
Easy to misjudge what appears to be a easy stroll on the map or guide site. It's also easy when not on the paved pathways to sprain and ankle or otherwise get a minor injury.
I love j-Tree an our National Parks, but J-Tree is a nasty blend of tamed leisurely themeparkesqye pathways and crowds, mobs climbing the rocks along the roads and remote raw rugged wilderness in extremely hostile terrain.