No, it's about pure D code. Some (many) people just don't want a GC in their program and that's why they use C++. If they switch to D, they'll have to put up with a GC if any of their dependencies needs one, and the probability of that being the case is... high.
You disable GC for the whole program? And what do you do when one of your dependencies relies on it? Just live with a memory leak?
Bear in mind you're simply not going to convince anti-GC folks that you can have the "good aspects" of a GC without the bad ones, and they're the folks you're trying to market to. To many C++ programmers the only good GC is one that is absent. You can tell them they're wrong all you want, but regardless of who's right, it's always been a losing battle.
You're not understanding my point unfortunately. I never said you can't turn it off. I said if you do, and any of your dependencies expect it to be on, then you have a problem. (Yes, I have tried D. That's how I know this.)