A simple answer is that there was more surface water and helped keep it cooler 150 years ago.

For example, I lived in Tucson, AZ and there was a road nearby called "Silverlake" that at one time led to a silver lake with enough power to support a flour mill (see https://tucson.com/news/blogs/streetsmarts/street-smarts-sil...). Now it leads to apartments and houses and an Air Force base.

More people + less water = hotter environment, even before climate change is factored in. A huge amount of the water in the area goes to agriculture as well.