What prompted Avraham to move his tent?
Rashi #1: Since the four major towns no longer existed, no more travelers passed by his tent. 1
Rashi #2: To distance himself from Lot, about whom rumors were spreading that he had relations with his own daughters. 2
The Seforno adds that Avraham now set up his tent between two big towns, in order to attract travelers from both towns, in order to spread the service of HaSh-m. Also refer to 12:8:2:1.
Riva, Moshav Zekenim (to 19:37), Ramban (to 19:32): Even though a Nochri is permitted to his daughter, the nations had separated themselves from Ervah. This is why Horayos 6b says that Lot's action was an Aveirah.
QUESTIONS ON RASHI
Rashi writes: "'Avraham moved away from there' - ... There were no more passerby... or, to distance himself from Lot." What was difficult with Rashi's first explanation?
Gur Aryeh: If Avraham moved only due to the destruction of Sedom, this verse should have been written earlier, before verse 19:29 (as soon as Avraham saw that Sedom had been destroyed). Rather, the Torah first concludes the account of Lot, to show a connection to Avraham's move.