No, its because the worgen (and goblin) starting zone is tied to a specific chain of events, in a very specific point in time, in a specific location that is entirely isolated from the rest of the world, set in the pre-pandaria era.
If they updated the starting zone, worgen would just be eligible for the monk class as everybody else.
Because in-universe neither of those are tied to very specific and very isolated incidents.
Both Azuremyst and Eversong are still part of the greater world around them and are utilized as such.
That the zones are old and outdated is just another gameplay limitation.
A Pandaren visiting Azuremyst or Eversong requires no in-universe explanation, they simply had direct access to those zones.
A Pandaren teaching a bunch of gilneans the ways of the monk before the Greymane Wall fell, and Pandaria was ever discovered, is gonna require a lot of jumping through hoops and loops to make sense of.