Elona's burried in the desert. Cantha?
You seem to be mistaken about something.
Elona is not the Crystal Desert. The Crystal Desert was what separated continental Tyria from the nation of Elona. Arguably, geographically speaking the Crystal Desert is part of Elona, but politically Elona ends – well, prior to Joko’s reign – at the Crystal Desert’s borders (note: the Desolation is the southern edge of the Crystal Desert, arguably). With Joko’s reign however, political Elona now reaches into the Crystal Desert.
Even in GW1, the Crystal Desert was a wasteland. However, in the past 250 years thanks to Joko damming the Elon river, much of the Crystal Desert and the Desolation – mainly around the river – has become verdant.
Elona is not abandoned but under the reign of an undead lich. Those “last known survivors” were the last refugees before Kralkatorrik’s rise which cut off contact with Elona completely – said last refugees passing through 50 years prior to GW2 (roughly). Elona still exists.
Cantha, too, still exists. Though we know not the state it is. We only know it exists because sporatic sailors wash ashore the Tarnished Coast – showing that they have ships being sent out for one reason or another. Zhaitan – and possibly the deep sea dragon – had been preventing contact with Cantha. The last we knew was 100 years prior to the game, and the continent was by all indications still the xenophobic mostly-isolated continent that it was since Usoku took the throne.
Stop treating GW2 as a single story. Each Season and expansion should be their own story.