PvP is terrible for the same reason people find PvE to be terrible, it's repetitive and boring if you don't enjoy playing the same 3 maps for a year or more straight. Personally for me I don't enjoy waiting 10 minutes in a queue to play an arena match that lasts 30 seconds to a minute, only to hop back in that 10 minute queue another 9 times to get points for the week. My main has zero pieces of s3 (all s3 honor items, 2pc s2 and 1pc s1) yet I can hit 1820 in one night queing up with some guildmate alts. For people who know how to handle their opponents and what counters certain classes or specs PVP is a breeze. I should get into arena on my alt warrior because it's the easiest way to gear it up, but I just don't get any pleasure from it.
I simply prefer the randomness of world PVP or BG's when people are equally geared (offering a fair fight) since it's not always the same shit rehashed over and over. It's unfortunate that Blizzard killed the drive to compete in those areas though in favor of having 100 copies of the same specs and similar setups duking it out in 10 minute queues.
Some PvE encounters are easily harder than playing arena, depending on how your guild tackles a boss. I know the way we do Illidari Council if you catch a stroke of bad luck with garrote, flamestrike or blizzard you can go from 100% to dead in about a second. It's akin to moving out of LoS of your healers and getting gibbed in the open. The Sunwell encounters so far are even more demanding than the hardest BT fight with enrage timers, dps benchmarks and coordination involved in taking down some encounters. You have your challenges and I have mine, but many of the people claiming superiority in arena are the same ones that /beg /plea /no when I'm bored and find them out farming. Yes, I die as well - but I don't ride in on a huge ego, I simply ride in and chop theirs down.