Simply providing people water would go a very, very long way to helping, and is a change that could happen literally overnight- if someone cared enough. Like the people running the Masjid al-Haram that surrounds the Kaaba, or Makkah city officials….
Sure it would be expensive. But how much money do those entities (as well as the services that arrange pilgrimage stuff like a vacation,) make off the Hajj?
With people dying “even in hotels”, keep in mind that if you reduce the worst exposure (standing out in a crowded place in direct sun with no access to water…) then you can suddenly tolerate a more-but-not-as-bad exposure in the hotels.