Because there is no reason to. Mainspace articles do not have much (if any) added value on this wiki, and the prevent users from creating or editing mainspace articles on this wiki, this is generally not possible. Of course there are still articles left on this wiki, but these are mainly left over from Fandom University.
No, that isn't what "hardcoding" means. If you can add a topic to a talk page, you can edit/delete other content on the talk page. That is one of the main reasons they are not considered a good alternative to article comments.