Because of pervasive ass-covering in the kinds of organizations responsible for this kind of messaging and infantilization of people just in general they just put a "pls don't do the thing you're here to do" sign that everyone will ignore rather than an informative sign and "make your own decision" that might actually help a few people think twice about doing something actually dumb.

Even in the heat, it's not a particularly long hike. Morning or evening wouldn't be an issue. That said, it's not like the majority of tourists show up early!

The people who need the signs aren't the ones who are paying attention to conditions. I never head out without either checking the weather myself or knowing that a person whose judgment I trust has checked the weather.

Just drove down CA 50 this morning in all the snow, and a good portion of road signs is out of whack: 55mph limit signs are a joke when you have the mandatory chains on, 35mph yellow signs are a joke in the summer, seems like they are trying to come up with some "average" values safe all-year-round despite winter and summer conditions being complete opposites.