I play a protection paladin as well, and I fully agree with you. I wish I had discovered how fun tanking is long ago, before I spent 2 years DPSing and Healing as various classes.
I'd say a lot of people don't like tanking, because it makes you have to focus a lot, and when running tens of instances every week, it can get a bit tiresome, and if you find a bad group, it usually ends up being either the tanks fault, or the healers, and really, no one likes getting the blame. Another problem, at least that I've felt during my time as tank, is that when it comes to raiding is that guilds simply need less tank than any other role, and as a tank, the role you of course want in the raid, is MT, but there can only be one MT in each raid, and most guilds try to keep to have one single person in the guild as MT. No raidspot / the raidspot you want would in the end make you respec to a spec where you do get to raid.