Adultery Law Stays on the Books

This week NH representatives voted to keep a 200 year old law outlawing adultery on the books in NH (HB 1402). My question on hearing this is why?

A person is guilty of a class B misdemeanor if, being a married person, he engages in sexual intercourse with another not his spouse or, being unmarried, engages in sexual intercourse with another known by him to be married.

Any idea when the last time this law was enforced?  Is anyone aware of any married person who suddenly choose not to cheat on their spouse in NH because of this law?

Why then choose to keep a unenforced useless law on the books?  What's the point?