Because we are about to destroy this place, for
its outcry before G-d has grown great, and G-d
has sent us to destroy it.
Genesis 19:13
There were five cities that G-d intended to destroy on account of their wickedness. Sodom and Gomorrah were destroyed by fire that descended from heaven; Admah and Tzevoyim were overturned (by an earthquake); Tzo’ar was spared at Lot’s request that it serve as a refuge for him and his daughters.
The reason why Sodom and Gomorrah were destroyed by heavenly fire while Admah and Tzevoyim suffered a less horrific fate is because the former two cities were guilty of having made mistreatment of their fellow human beings an essential part of their culture.
The latter two cities, in contrast, sinned primarily against G-d, and less so against their fellow human beings.
This teaches us that G-d is more concerned with our treatment of our fellow human beings than He is with our respect for Him. As the Talmudic sage Hillel said, treating your fellow human being as you would like to be treated is the essence of the Torah; all the rest is commentary.
--Daily Wisdom Volume 3