I believe it's necessary especially when one party needs or deserves to know the reason of the break up. Some people whose lovers have broken up with them need to hear an explanation because 1) they could learn from it so they can 2) avoid doing that mistake in their next relationship and 3) it's for the sake of their sanity. As for the people who broke up with their lovers need to offer the explanation because 1) they might feel less guilty about it, 2) they are humane enough to feel that it's their responsibility to end it well, and 3) to avoid crazy ex dramas Although I tried offering an explanation when I broke up with an ex. She didn't want to hear it and I felt a bit taken aback. It actually felt like my act of respect was rejected. I listened to her and didn't explain further. So yeah maybe it's not necessary for some people. Why they think so, I'd really like to know why.