Writing a post in which one sums up the problems one has with the game is a nice way to rationalize, or justify to oneself, the decision to quit.
Note also that unlike most other games, MMOs often involve groups of people with which one interacts on a regular and perhaps even scheduled basis. It's also common courtesy to not just leave and keep everyone guessing as to what happened.
Because they're paying a monthly subscription fee and see preciously little in return.
Other big MMOs have shown a monthly fee is not necessary to maintain the hardware infrastructure of the game.
Maybe at one point it was, and I've certainly played my fair share of characters. But if you combine a variety of changes such as much easier levelling, much quicker levelling, much more homogenized classes, and the fact that some parts of the game are at least nine, if not eleven years, old it should be little surprise why starting new characters has lost most of its appeal to people who've been around for a while.