Even though some players don't raid, for about 60-70% of players raiding is the end game.

Blizzard did several things at once in Cata. They changed healing and tanking mechanics, that drove away many players from those roles. If you are lucky to be in one of the top 5 guilds on your server you probably didn't noticed the lack of tanks and healers as much since your guild had a strong draw for recruiting due to progression and reputation. For all other guilds it was painfully obvious that these roles were in short supply and raids were hard to put together for lack of these roles and guilds fought over players in these roles.

If a guild was a car engine, this was like dropping a handful of sand into it.

Another change was adding healer mana as a type of second soft enrage for all raids, now not only was DPS before the enrage timer a factor, but now so was healer mana.

And finally, the player coordination factor of raids were increased. Most had some gimmick that required almost everybody to do it almost perfectly or the raid wiped. This seems to have been implemented as AOE damage penalty in most cases. Everybody does not move out of the flame pillar on magmaw, or everybody does not switch dps on ODS to prevent shield breakage...

To raid you not only needed mostly competent players, now you pretty much needed all of the players to be competent, just one slow, laggy, or 'sandwich eater' as we used to call them in MC days, and the raid wipes.

And finally the gearing up for raid grind was possibly the worse it has ever been, if you actually wanted to get all the gear from heroic 5 mans that you could before raiding it was 6-12 weeks of grinding for badges depending on how much gear you wanted vs. how grind you could stand.

What was the result of all this, well for blizzard it meant that players would take longer to complete content, good for them, less work for the same amount of money coming in.

For players, raiding was much less fun all-in-all than it has ever been. Sure some guilds cleared content, a very small percentage of guilds. Many players, those healers and those tanks who didn't like the new mechanics, the 'sandwich eaters' who now wiped the raid, the people who were forced to sit on the raiding bench for lack of healers or tanks to form raids with, all of them were losers in this expansion.