Have you ever tried to read a math textbook that cherishes being short and concise? They're nigh unreadable unless you already know everything in them. When you're discussing simple concepts that people have an intuitive grasp of, then brevity is better. When there's an inferential distance involved, not so much.

I don't know about others, but it helps me understand an idea when I read a lot of words about it. I think it causes my subconscious to say "this is an important idea!" better than reading a concise, densely-packed explanation of a thing, even if only once. This is a guess; I don't know the true cause of the effect, but I know the effect is there.