The TBC dungeon tool basically listed you as wanting to do whichever dungeons/quests and relied on other people listing themselves in the tool/looking for others in the tool. Was mostly useless, but it did exist, just not in the queue and go straight in version implemented in 3.3
ALL healers being ridiculously op have caused a boom in healer numbers it seems to me.
fixed that for you.
Ever since Blizzard turned on godmode for healers way back in BC their numbers kept rising steadily.
Healers are (relatively) fun to play now in PvE and by far the most potent and noob-friendly classes to play in PvP (especially druid and pally) - all while still being able to be a fully viable - or even top of the foodchain - DPSers if you so choose.
The only pragmatic reason not to play a healing capable class in this game is that warriors cant be healers ;-)