This is indeed down to how Word represents the text as HTML - it's not actually a list, so it doesn't get converted as one. It uses some properties like text-indent or margins that are quite hard to translate (to the limited set of BB code), as well as some Word-proprietary ones (mso-list), combined with using fonts like Wingdings to represent the bullets.
We might be able to translate the margin/text-indent, though that's a big challenge, but since it's not submitting as a list, it's not really feasible to translate to a list.