Judged like a Tzaddik

The Midrash, quoted by Rashi, says Lot was saved from Sodom because he kept silent when Avraham told everyone that Sarah was his sister. That seems backwards. Silence about his own uncle hardly sounds like much, while the Torah spends so much time on Lot's open home for guests. Why did the quiet act outweigh the visible one? It leads to why Amon and Moav were barred from the Jewish people, and to what Hashem expects from each of us in Elul. A friend's phone call about his mother's illness and a sum due the next day closes it.