It's a tricky situation I think.
On occasion, I think the forum can get a little heated. I would guess that if you were someone whose work was the subject of those discussions, it might not be a very comfortable experience. I'm not referring to the constructive criticism when I say that, because every dev should be able to handle it to a degree, but I mean some people can be extremely passionate and occasionally lose their heads when decrying a feature (and I think we all do/have done this). So, on that end, I can understand why some devs might prefer to have other people sift through the threads and report back to them (I would guess that there's nothing in the contracts of the employees that say they have to interact on the forums. It's their personal choice)
That's not even touching the issue of PR related things. How much is an employee allowed to share? What if an employee says something, it gets misinterpreted for whatever reason, and people on both sides get annoyed? Not a fun occasion, I'll bet.
I too, would greatly like to see them return to making more regular posts and engaging with the community, but at the same time I can empathize with why they might not want to. I do think that they are observing, even if we're not seeing some of the more well known names pop up as often. After all, it's a bit of a waste of money if they don't utilize these forums for something, no? Perhaps I am being optimistic, but seeing as its something I don't have control over, I'm content to assume that someone is seeing what we're writing, and maybe even taking some of it into account.