I was just talking about this with my friend the other day.
Part of it is obviously the Blizzard's fault, they "force" many types of players into the same content basically, you have people who've dinged day1 and now farming the leggos in full m0 gear and trying to do the runs as fast as possible, and the "weekend warriors" who are still levelling (or have just dinged) and are in the dungeon for the first time.
Imagine doing De Other Side, lore-heavy dungeon with some interesting info, but the tank is chainpulling everything. Nobody even bothers telling you what to do on the last boss (but shame you when you don't do the portal). It's a crap experience, for some reason people expect everyone to be "on their level" and to "get on with it", even though there are many types of players experiencing the same content.
You also lose the fun of discovering the mechanics. The first m0 runs, where you go blind with your group and figure everything out is the most fun dungeon experience you can have. But to get it you basically have a time-window of 3-5 days. Week 2 - zerg everything.
The solution, as usual, is a guild of like-minded people that play at your pace. Obviously it's hard to avoid pugging, since LFD system is so convenient, but do yourself a favour and find a guild. This is how WoW is supposed to be played.