Doesn't matter what the state the dungeons are in when they reward experience more quickly and better items than PVE. If you get in a decent group you can bypass entire PVE zones in relatively short order. Which is why people are spamming the queue in the first pace. They don't want to play through the same old zones doing the same old quests for crap gear and little to no reward.
People follow the path of least resistance. I do not think it has anything to do with people being bored of the old zones by and large. If you are leveling you have to deliberately slow yourself down to a crawl to even engage with questing through zones. People spam the queue because it can be virtually instant, and you don't even have to consider what level you are. It will immediately bring you to relevant content. Travel time is suddenly a non-factor. Quests are delivered to you up front and are streamlined down the dungeon path you were taking anyways.
Compare that to questing through zones, where it's easy to outlevel the content around you and find yourself unable to follow the storyline, attain the higher rewards offered deeper down long quest chains, and endlessly trekking to relevant content. Surpassed the content in Southern STV? Enjoy finding your way to Dustwallow, Feralas, or WPL.
As a player, it is impossible to justify spending the time to run out to locations that are rendered obsolete soon after your arrival. The alternative is sitting around a city will full access to amenities while the game teleports you to the most efficient EXP gains imaginable. I do not think it is explicitly fatigue that deters people from old zones. They're certainly not exciting, but dungeon fatigue is probably more real at this point. It is literally impossible to see most zones through without hamstringing your own pace. This is the boon of the scaling level system. It actually gives world content a chance to compete with where low level dungeons are at.