Don't you think that people who commit adultery should be incarcerated?

Because we do not live in a theocracy. If you want politics to be based on religious texts, move to Iran. I think you'll quickly see that it's not an approach that you care to live with. Well, Adultery technically can be punished. But not generally by a legislative body. Usually, the spouse (the one who is harmed in this situation) is granted extra leeway when filing for divorce. But the onus is on the partners involved in the relationship to seek a conclusion between them.