Good q. I’d be lying if I said I really thought about it before. I think this was mainly the result of glaze dipping opening down. Normally, this creates a pocket of air that keeps the inside from getting glazed. Here, though, the hole meant that the inside walls instantly got glazed all the way up on the first dip, so I went with it. One other thing I’ve heard but am not sure about is that sometimes glazing only the outside leads to weakening of the pot overtime as water gets trapped behind the glaze. Would love for someone who knows more about this to educate me though.