Abraham was unique even among his blood kin. He is the only one who wasn’t an idol worshipper. Even he was marked by the culture he came out of. What was different about him is that he sought God from the heart and responded when God spoke to him, though there wasn’t much in the culture to tell him who God was.
When you think about it, Noah was God’s man, but his offspring were apparently not. Within only a couple of generations of the flood, much of the evil that existed before was back, and the God of Noah forgotten. But then there was Abraham.
God clearly spared Lot only for Abraham’s sake.