They do it because it is easy, it allows you to live through inaction and avoid all confrontation. As many church goers never actually engage with the material, this appeals to their sheep like mindset. Something I find especially prevalent in Catholics, at least in the US. They go to mass, vaguely read the book (either once or the same few passages they are biased towards) and then talk a high game, but never when the chips are down.

Enabling someone to continue into sin is just as sinful as the deed they commit, and so many followers of Jesus are guilty of enabling beyond forgiveness.