Probably they're just experimenting on which routes can sustain a VB. That's a different issue that they're failing in most of them. But a lot of routes will ultimately catch up.
Bombay-Hyderabad may need a sleeper version I suppose. No one would like to travel that much distance sitting.
I...
more... think the over the top PR of VBs have snatched the passengers from Shatabdis. Because even Tejas was a new concept and we all know the fate it met. I think VBs are priced as such that they don't even need dynamic fares.