Lore wise this did change after the Siege of Orgrimmar, as revealed in A Good War that the Horde had removed themselves from Ashenvale in accordance with the treaty thereafter.
Speaking of said treaty, Tyrande did not cede Azshara to the Horde, only allowed them the use of its lumber:
I am willing to allow the Horde the use of Azshara’s lumber if they abandon Ashenvale for good.
The Night Elves did not abandon Azshara, as was shown during the Legion Invasion pre-expansion events, where we saw the Talrendis Ancient had grown back, and Night Elf forces were still stationed in Azshara, and both helped the Goblins fend off the demons from the back gates of Orgrimmar.