There's a reason for this. The high heat makes the air less dense, meaning there are less air particles around the wing of the plane. The plane needs to go even faster to achieve lift in this case. Sometimes there's just not enough runway to make this happen.
This will hurt a city like Las Vegas more than most since a lot of locals work at casinos and hotels, with fewer patrons that could mean fewer tips and fewer dollars in their pockets.
Tourism supported 391,000 jobs last year in Southern Nevada, according to the Las Vegas Convention and Visitors Authority.
It's up to the airline, not the airport, to decide to fly. The rules about heat and take off change from plane to plane.