Genesis 19:30-33 meaning

Lot went up from Zoar, and stayed in the mountains which was the original instructions given by the angel (verse 17). Lot might have feared the inhabitants of  Zoar. He might have enjoyed some immunity in Sodom, where his uncle Abraham was known as a formidable warrior, and a protector of Lot. Perhaps in Zoar he did not enjoy that reputation. Whatever the reason, all we know is that he was afraid to stay in Zoar. At one time, Lot had "flocks and herds and tents" (Genesis 13:5), "great possessions" (Genesis 13:6), and many "herdsmen" (Genesis 13:7-8) and lived in a well-built "house" (Genesis 19:3-11); but now, having been delivered by the mercies of God, his household was reduced to three people and he stayed in a cave. 

The two daughters lost their fiancé's in the destruction of Sodom and were deprived of husbands and children. Therefore, there was no one to preserve their father's family line. They observed that their father is old and there is not a man on earth to come into them after the manner of the earth. They were not lustful for their father but rather used him as a means to an end, namely pregnancy. They desired an heir to continue their family line. We see widows seek an inheritance in a number of biblical stories, including the stories of Ruth and Tamar, two of the four women named in Jesus' genealogy (Mary and Rahab being the other two.) 

So they made a plan to make our father drink wine, and let us lie with him that we may preserve our family through our father. It does not appear they considered going to Abraham and asking for help, including looking for a husband. The men in Zoar don't seem to be an option. We know the daughters had been exposed to a lot of moral depravity. They were prepared to marry in to the culture of Sodom. 

 Conversely, we are told that Lot was righteous (2 Peter 2:7). So it follows that the girls  knew their father would not have approved of their plan, which is why they had to trick him with the wine. 

So they made their father drink wine that night. Lot became so drunk that he did not know when she [the older sister] lay down or when she arose. It seems that the girls have a considerable ability to sway their father. This could explain why he remained in Sodom, and was reluctant to leave Sodom.