Why does Thoreau say John Field gives up considering the possibility of a more simple life?

This is actually from Walden but I suppose there are shades of it in Huckelberry Finn. While on an afternoon ramble in the woods, Thoreau gets caught in a rainstorm and takes shelter in the dirty, dismal hut of John Field, a penniless but hard-working Irish farmhand, and his wife and children. Thoreau urges Field to live a simple but independent and fulfilling life in the woods, thereby freeing himself of employers and creditors. But the Irishman won't give up his aspirations of luxury and the quest for the American dream.