As well as the decent reasons for being proud not to learn more about a topic, where I have come across it most often is when people can win the argument otherwise. e.g. as I am trying to explain a hole in their position their eyes glaze over (or stare mockingly), and when I am finished speaking they proudly reassert their original position.

Might be pride in their own certainty, or pride in not feeling obligated to listen.

Maybe some pride in being unknowledgable is a special case of pride in having beliefs with high inertia.