Why household life is compared with dark well?

In household affairs the first attraction is the beautiful and pleasing wife, who increases household attraction more and more. One enjoys his wife with two prominent sense organs, namely the tongue and the genitals. The wife speaks very sweetly. This is certainly an attraction. Then she prepares very palatable foods to satisfy the tongue, and when the tongue is satisfied one gains strength in the other sense organs, especially the genitals. Thus the wife gives pleasure in sexual intercourse. Household life means sex life (yan maithunadi-grhamedhi-sukham hi tuccham). This is encouraged by the tongue. Then there are children. A baby gives pleasure by speaking sweet words in broken language, and when the sons and daughters are grown up one becomes involved in their education and marriage. Then there are one’s own father and mother to be taken care of, and one also becomes concerned with the social atmosphere and with pleasing his brothers and sisters. A man becomes increasingly entangled in household affairs, so much so that leaving them becomes almost impossible. Thus the household becomes grham andhakupam, a dark well into which the man has fallen. For such a man to get out is extremely difficult unless he is helped by a strong person, the spiritual master, who helps the fallen person with the strong rope of spiritual instructions. A fallen person should take advantage of this rope, and then the spiritual master, or the Supreme Personality of Godhead, Krishna, will take him out of the dark well.

Source: A.C. Bhaktivedanta Swami Prabhupada (2014 edition), “Srimad Bhagavatam”, Seventh Canto, Chapter 06 – Text 13