I heard that too many people from fall 2014 extended and/or they hired too many people for spring 2015 at WDW to the point where they had to ask some people to push back their move-in dates. Maybe they're just limiting the number of people that extend to prevent this from happening again.
Also, at least during my CP, it depended on whether or not you chose Same Role/Same Location or New Role. I remember the Extension application HEAVILY indicated that those who chose Same Role/Same Location would have a better chance.
All four of us in my Role/Location applied. My best friend and I were the only two offered extensions, both in the Same Role/Same Location.