I don’t personally understand, still even it has been explained, point of nil content, but it is just my opinion. If an admin wants such feature and users are using it, why settings aren’t approving zero?
I mean is there lying behind something similar than with multiple drafts that are several times asked, but aren’t coming because of structure of Diacourse? So it would be more complex job than just changing some value in the code?
If it is practically impossible to allow because it would need huge amount of work then the situation would be more acceptable. And after that such forums could start using those tricks, that messes toolbox or users must remeber tricks to make something work. In both cases it breaks the idea give ability use only headers easily and without touching content itself. All of those tricks are just quick fixes, though.
But if the reason is more politically or strategically then I would ask if a fear of image of Discourse as serial forum platform in the eyes of big companies is really threated because of some forums that has its conversation happening using tittles and headers? Why are then allowed discuss using hieroglyfs and gifs 
Because it sounds like that now.