Because contrary to what you seem to believe the content prior to raiding doesn't require wiping a bunch of times till you figure it out. Worse case you get a friend help you with a class quest.
But again, your answer seems to be to have 90% of the population go play something else. Which is all great and all except for the servers will shut down and you won't be playing either.
What I believe is that content should be challenging not that 90% of the population should go play something else. In fact some content in many other MMOs before raiding DID require you to die a bunch of times to complete it, or to figure out what you were doing wrong. It taught you how to properly play your class and to pay attention to what is going on. That is gone now, allowing people to faceroll their way to 50, or for some who can't even manage that to call a level 50 friend in to do it for them while they autofollow, and then walk into a tier 2 raid expecting to do the same. If it doesn't require some effort what is the point of having it there anyway? If, spending a half hour to an hour learning what is supposed to be the one of the harder encounters in a game is to much for people where the **** is it going to end?
Let's try something:
Let's say that yes, raids are to hard right now so we nerf it down a bit or a lot depending on your viewpoint. We get one of the guilds or pugs or whatever it is to try it.
"Well we beat Story mode pretty easily, let's try hard mode"
They get *********** DESTROYED.
They come back here and state, hard mode is to hard it needs to be easier.
Since story-mode isn't difficult enough anymore to challenge the player and make him think and react to prepare him or her for hard-mode Bioware has a few choices:
A: Make story-mode harder -> the guilds go back to not finishing story-mode and quit or complain or whatever
B: Ignore them -> .... actually I don't see a downside to this one
C: Nerf hard-mode down so it is doable for the "Casual Player" -> and soon to follow nerfing Nightmare-mode and so on and so forth.
tl;dr: Game is easy enough with some effort, make it any easier and it will not require any effort.