There are a few reasons we don't allow this. One of course, as you pointed out, is because it's a paid function of the platform (creating a topic), however we also have people responding who are simply outdated in knowledge as their software is not up to date, people trying to respond to others tickets to point out they have the same issue as another person and trying to gain support that way etc.
So realistically, while I can certainly see your point there, its unlikely we would change that as this point.