As I understand, the identity of Azir is one of a hyper carry mage with incredible damage and positioning ability. However, throughout Azir's history, his defense has been a tad too solid for a mage that can do 150k+ damage in thirty minutes on a bad day. That's why they took away his knockup portion of Shifting Sands: it was too all around useful. It gave a shield, CC, and potentially moved Azir into a position where he could destroy your backline or escape a gank.
So, in order to minimize the damage to the most fun aspects of Azir's gameplay, while also reducing his pick/ban rate, they took another jab at his defense this latest patch. When you play Azir, you want to control enemy movement with oppressive amounts of damage and a force push-esque ultimate. People don't really identify Azir as the "put up a wall and hide behind it" bird champ. That's Anivia. So that part of his kit was expendable. What was more important was preserving his ability to change map positions rapidly and deliver incredible damage to players.
The patch podcast did a really good job of explaining it, I think. In order to promote champion diversity while also maintaining the qualities that make Azir AZIR-ish, they had to make some sort of weakness, and they handled it well, with less damage to turrets, slower game power up with Nashor's Tooth (higher combine cost and stinger nerf, but no cost increase altogether), and finally reducing the unkillability of everyone's favorite sand emperor.
Nice job, Riot.
