Image hosting is so dirt cheap these that it’s not usually much of a pricing concern. It’d cost you maybe $1-$2 per 100 GB. At Discourse’s scale, it’s probably much cheaper, and the forum admins can configure a bunch of settings to limit storage. Anyway, we had a whole other thread about that, in which the consensus was “it’s more of a bureaucratic hurdle than a technical one, and we don’t want to risk our owners having any second thoughts about our forum at all” (which makes sense).
As for the bug report, well, it doesn’t take much to make it happen… you can just sign up for a Discourse trial (no credit card needed), follow the few steps on that bug report, and make it happen for yourself (I did).
It probably just is an uncommon setting… “images in my forum or not” was more of a 1990s and 2000s concern and hasn’t really been much of an issue since.