The reason behind the lack of healers compared to WotlK was because of the level of difficulty of heroics in the start of Cataclysm. Alot of healers said that they quit the game because healing was so hard and you had to drink after every trash pack, while puggers still pulled the next pack and shit.
In my opinion they were just bad healers. Ofcourse I whined a bit aswell. But that was mostly because the reason I had to drink all the time. It took like 2 days of Heroic farming and that wasn't really a problem anymore... And people that says that healing is harder now than it was in wotlk are bullshitters. Healing is not harder than it was.
But that doesn't explain why there aren't enough capable healers on your realm. The healers that are still in the game are the healers that made it through the heroics without quitting the game. So technically they should be better than those who quit or rerolled. Some probably rerolled to healers after the heroic nerfs and LFD buff. But the majority of healers should be those whose main is a healer, and which they leveled the 7th of December.