Which is part of the problem. If RSVP could do the advising you mentioned above, it might be able to somehow patch up the problem. Or the routing protocols could themselves be updated. As it is, I don't see how QoS can be achieved with RSVP over the existing, mostly non-RSVP Internet. Router vendors do tend to add new features and provide new software releases every once in a while.
Customers occasionally install the new releases.