I think what it all comes down to is most people don’t really want rational debate, and don’t participate in debates in the hope of learning or even to help others learn. Most people participate in debates to feel superior/“own” the other side. The result is debates that are typically lazy, uninformative, and downright mean.
I think all of us have a little bit of this desire for superiority in us and we need to consciously make an effort to suppress it.