With the Spy no longer seeing Mafia chat, having the VH seeing Vampire chat is extremely unintuitive - it's not something people would logically expect from his role, leading to a lot of frustration for (and from) new players who out stuff.
All the arguments for the Spy not seeing Mafia chat apply to this situation as well; the VH already has powerful abilities for dealing with vampires, while the restriction severely limits that chat's value. Vampires have even more need to communicate than Mafia in some ways (because new Vampires may not be aware of what the older ones have discovered, or may have stuff to share that they learned when alive), yet the VH hearing the chat makes all that less useful.
And the VH hearing Vampire chat is much more devastating than the Spy hearing Mafia chat ever was. The VH can kill you directly (even that very night) if someone slips up. There's very little value to "tricking" him (at most you might make him waste a night; you can't cause a mislynch or anything.) Unlike with the old Spy mechanics, even your targets have to be kept secret from the VH, meaning there's almost nothing you can safely discuss.