וַיִּקְח֨וּ אֶת־ל֧וֹט וְאֶת־רְכֻשׁ֛וֹ בֶּן־אֲחִ֥י אַבְרָ֖ם וַיֵּלֵ֑כוּ וְה֥וּא יֹשֵׁ֖ב בִּסְדֹֽם׃
Tomaron también á Lot, hijo del hermano de Abram, que moraba en Sodoma, y su hacienda, y se fueron.
Rashi
והוא ישב בסדם FOR HE DWELT IN SODOM — What made this happen to him? The fact that he was dwelling in Sodom (Genesis Rabbah 42:7).
Chizkuni
והוא יושב בסדום, “and he dwelled in Sodom;” note the singular mode; none of his relatives lived in Sodom. This accounted for his being taken captive alone. Alternate explanation: he entered the city now that he was afraid of being solitary against the warring nations.
Sforno
ויקחו את לוט בן אחי אברם, they made a special effort to capture Lot because he was Avram’s nephew. They were aware of his wealth. They were expecting that Avram would pay a heavy ransom for the release of his nephew.