I think it's not so much black and white as accepted or denied.
For my own projects I have more ideas that I would love to implement than I have the ability to do so. Add outside suggestions onto that... And with the immense volume of suggestions possible from the interwebs, all the time spent triaging suggestions is time not spent implementing them.
Even if I see an amazing suggestion/idea I didn't have before, I don't know how long it will take or how feasible it is to complete in a reasonable amount of time (especially for the more involved, big suggestions - the ones that have a lot of popularity). I wouldn't want to promise something that I wasn't ready to deliver on.
Same for denied. If I love the idea, but I'm not going to do it ahead of everything else I'm doing at the moment, I wouldn't want to straight up deny it. Also if it can gain traction and more and more people down the road are interested in it, I'd want to leave it there for that possibility and not just say denied.
The idea of promising something I am (or not) ready to deliver is related to disclosing what is actively being developed, which can actually be seen pretty clearly in the betas. Often there are many things being worked on a time, which may gain or lose priority, but if something like the 3d object is ready to be committed to, it will show up in a beta. And if it's in the beta, that's prooooobably what they are working on right now to get it ready for release.