I'll be honest, leveling a healer started way back in HW when i was trying to finish a DRG Relic. Queues were faster then and it was a no brainer for trying to get it done. (I still haven't finished that relic *snorts* i need my dragon on a stick, i'll get it, eventually) Now however, I main Healer because I want to. I enjoy being the one that has to figure out exactly what a mechanic is going to do and if i need Single Target or Group wide Healing. It's also a good way to get rid of daily frustration. Log in, queue up, throw stones and Wind Bombs at mobs, get frustrated and realize how trivial everything is and start snickering and giggling about my mistakes and the mistakes around me.
Also, my FCmates look at me as kind of a savior, they don't have the patience to do anything other than Tank/DPS for the most part...and they're all leveling DPS. as a crafter (that's my end game, not savage raiding) I tend to poke them for mats if i'm in the middle of crafting, so in return: i give them my queue to level. So...I'm helping others as well.