The more private a debate, the more likely people will be generous enough for this to happen; the more public, the more hostile they will be. Hostility is a status-grab, and people in arguments (including this forum) reward it if they think the grabber deserving. Similarly, generosity is low-status, and people who are generous in public debates have very little to gain. Publicly failing in the quantity necessary to maximize your learning growth is very low-status and not many people have the stomach for it.

EDIT: Being low-status also makes it much easier for people to stop responding to your arguments, as "That's not worthy of a response" is much more believable from the higher-status arguer when the status difference is high.