Why did Abraham speak to the LORD for Sodom and Gomorrah?

Less than 23 years prior, Lot and then Abram had separated because both of their possessions were so great, and Lot chose to live as far as Sodom. Early on, he had been taken captive during the war of the kings, but Abram took 318 trained men who were born in his household and rescued Lot with his possessions, and the women, and the people. So, as years have passed and God informs now Abraham he is going to destroy his nephew’s city, he asks for a “modest” fifty. When he receives the response, the following requests I believe are Abraham assessing the gravity of the loss his nephew has faced over the years as he remembers separating because of the abundance they both had and now Lot doesn’t even have nine others that can be vouched righteous enough to spare the city.

References

Genesis

13:6 their possessions were so great

 13:12 Lot chose Sodom

 14:12 Lot taken captive

 14:14-16 Abram rescues Lot

 16:3 After Abram lived ten years in the land

 16:16 – 17:1 Abram was 86 years old – Abram was 99 years old (13 years)

 18:20-32 Abraham speaks to God for Sodom and Gomorrah