Its an extreme event for the average person. Lots of folks are unaware of the danger of overhydration. Combine that with local races where people might be doing their first attempts at longer distance and this starts to become a problem, especially in hotter climates.

Every year there are people that sign up for races with no prior experience thinking "meh, I could run a half marathon". Guess who shows up with a ton of water, no food, and no electrolytes. The same folks that think they could take a bear in a fight. 🙄

I fully agree that HMs are not considered an extreme event by any standard. Many people are running this distance as part of their weekly workout schedule.