Why is server stability such a bad thing? You know why they did it. You saw the posts about how the Zepplin wasn't working, Orgrimmar crashed, people being trapped on Draenor or in Oribos.
Theyturned on hard sharding to alleviate it it, just like they announced they were going to do for Classic's launch. And, just like the Classic servers, they'll tone it down as things settle and eventually the servers will just do it dynamically on an as-needed basis.
Also, you're not seeing people because they're zipping around everywhere on their dragons.