I know we're going to get comments like "boring, rehashed content. Instead of adding permanent content, they just reuse old content and try to pass it off as new."
But there's one huge merit to this model that just feels so darn good: when it's temporary, and when it only comes around once every so often, players get excited all over again. There's a buzz in the atmosphere as everyone rushes to participate in the content. When you go there, it will be absolutely hopping with players and activity.
Imagine, on the other hand, if it had been released permanently? How many often would players congregate in Zephyr Sanctum? How often would they run the Queen's Gauntlet? Super Adventure Box? Answer: about as often as they play Keg Brawl or legitimately quest in Southsun. It would be impossible to get excited about going to any of those zones. Done this way, it will be exciting every time the events come around.
This also shows that Anet is paying attention to what content players enjoyed, as Bazaar and Crown Pavillion were by far the most successful bits of the Living World to date.
TL/DR: Temporary content creates excitement where there otherwise would be none, and brings players together. Yay.