Cheating is such a low effort easy way out type of changing one's preference. People sometimes want to have their cake and eat it or rather not having the discipline to stick to long term commitments.
I also think that telling the truth or being truthful is way easier, especially in the long run as eventually, what's hidden will be revealed and there's no coming back from that.
I completely agree, cheating must be a very unpleasant situation, so it's easier to tell the truth right away. Lost trust is difficult to regain later.