...then you're probably a terrible DPS.
Being able to "get away" with doing poorly doesn't mean DPS is easier. DPS is just as difficult as the other roles, but people are less likely to notice if you suck at DPS than if you suck at healing or tanking.
EDIT: Okay, since everybody in this thread keeps calling me a troll or someone who hasn't played all of the roles despite the fact I responded with a long post already, let me add that post to this initial post so you guys can stop assuming things that you have no clue about.
I never said DPS was harder than Tanking or Healing. I just said, when done properly, it's not easier. I didn't say DPS was more important than tanking or healing. You can afford to lose a DPS. You can't afford to lose the tank or healer, usually.
As for "stroking my ego" let me state that I play all roles. My shaman, enhancement. Druid, resto/tank. Rogue, assassination. Paladin, Prot/Ret. Priest, Holy/Shadow. DK, Unholy/Blood. I'm not trying to say my job is better. I have done and DO participate in all roles. I enjoy all roles. I don't pride myself in my DPS any more than I do my healing or tanking.
Yeah, I can go in with my rogue and use nothing by mut, snd, and envenom. I'll probably do reasonable enough DPS to where nobody will notice. Of course, I won't be sapping, kicking, gouging (as a quick interrupt when kick is on CD), using tott, and I won't even be doing a proper rotation, not using defensive cooldowns when I'm taking unavoidable damage. Yes, this is easy. But if I did it that way, I'd be doing it WRONG. People might not notice. Some might. But yes, it'd be very easy.
But if I start to perform properly, doing a more ideal rotation, using CDs, kicking, using crowd control, aggro management... then it becomes a little more challenging. And you can ALWAYS do better. That's why it's not easy. It should NEVER be easy. You should constantly be pushing to do the best you can, and you will NEVER be the best. You will never hit those simulation numbers. Which means as DPS, you have to give it every thing you have, and it still won't be enough. THAT'S why it's hard.
If you don't try, of course it's easy.
It's the same for tanking as DPS. Tanks have to get the initial aggro, maintain it, use defensive cooldowns when necessary, still maintain a rotation/priority list just like the DPS do, and interrupt when possible/necessary. But if you screw up, people will surely notice. So you can't screw up. But that doesn't make it difficult, it just means you can't get away with the same stuff people try to get away with when being lazy DPS. But as a tank, you have to make up for DPS not doing their jobs, and targeting the wrong mobs. It has plenty of responsibility as well. Again, you can't really cap out on this - you can maintain better aggro, time your cooldowns better, and you should be adding a good amount of DPS as a tank too - much like dps, this can always be improved.
Heals is a different beast - much like DPS you can never hit that cap. You can never be perfect. The thing about healing is that you always can improve, and if the tank and DPS are failing, YOU have the capability (not necessarily obligation) to compensate for them (barring 1-shots). It's also quite noticeable when you fail. But healers do get the brunt of blame because others might consider the fact hat the healers couldn't compensate for the others' failure to be a failure on the healer's part. Regardless, you will never cap out. Keeping people alive is one thing, but as long as you have bad dps and tanks to compensate for, you can ALWAYS improve.
My conclusion is that ALL THREE roles have room for improvement. You will never be perfect. And if you have room to improve, then all you can do is do your best. And if you're doing your best in any of the 3 roles, then it's as hard as it's going to get.
It's only as "easy" or "hard" as you make it out to be. If you give minimal effort, any role will be easy. But if you happen to be tank or heals, people will notice that more quickly. But if you give it all you've got, any role will be hard. And you will never be perfect, so there's always room to "give it all you've got".
The reason we have so many less tanks and heals than DPS is because people don't want to be blamed. DPS is not easier. It's about the same, but people blame DPS a lot less often than tanks and heals, so players opt out of those roles in order to save themselves stress. Perhaps if people were less critical and more encouraging, this would be less of a problem.
My TLDR point is this: if you think ANY role is easier than the others, then you just need to try to do your role better until it doesn't feel easy anymore. Until then, you're under performing. You can ALWAYS do better.
DPS shouldn't feel easy. If it feels easy, you're not pushing yourself enough.