Back around 1974, California was in one of its periodic droughts. In January, we had an unseasonable warm spell and I left before dawn on a hike to the top of Yosemite Falls (which was a trickle that year). I got to the top and had the entire place to myself. Knowing how the mountains can turn on you, I was prepared with the right clothes for sudden bad weather even though it was hitting 70 that day. On the way down, I saw the people you are talking about. Hiking to the top of a high Sierras mountain in January with nothing on them but shorts, t-shirts and sandals. No food, no water, no preparedness for anything
You see that sort all over the land. It is amazing that more of them don’t die.
Another one bites the dust: https://nypost.com/2022/09/06/hiker-dies-in-fifth-grand-canyon-death-this-year/
The desert is unforgiving.