Dying during Hajj has always been a risk historically. Imagine you’d make the way from Afghanistan or Gambia to Mekka in the time before cars and planes. People were on the road for years, and the roads back then were a very different story.
Also for nowadays it needs to be kept in mind, that people often safe up a very long time, to afford doing Hajj. So by the time they saved enough money for it, they are quite old, which increases the risk of dying from heat.