Is there though?
This video is from less than two weeks ago, for example:
This is from 5 months ago:
So I'm not really sure I buy "vapourware" about the 3D VTT. If you'd said that in, say, March, sure. But at the very least they have some kind of semi-functional product, which if the first video is correct, is considerably more developed than the 4E 3D VTT ever got to be.
Vapourware traditionally indicates a product that is purely talked about, or where only non-interactive demos are shown, and neither of those seems to be the case here.
I think the issue with 3D VTT isn't that it's vapourware, it's that it's unclear who the actual audience for it is. Ironically in direct contrast, Maps has a very obvious audience - DMs who use D&D Beyond, and who either use a VTT and aren't super-happy with it, or don't use a VTT (particularly because of how fiddly they are). I don't think Maps is even basically usable yet (it needs super-basics like drawing tools, but they're coming soon, supposedly), but at least the audience is clear.
It seems with the 3D VTT, WotC is simultaneously trying to maybe get groups who play offline or with other VTTs onboard with the 3D VTT, but also to maybe provide a platform where people who don't have existing D&D games can meet and up and play, all whilst encouraging the maximum possible spending on MTX bling, and I'm just not sure how cogent that vision is. I'm fairly confident that we will see a functioning 3D VTT, but whether it'll actually be worth using? Wholly separate question.