In patch 4.3 they removed the ability to buy set items with valor tokens, and since it's late in the expansion the set bonusses are really strong / good / cool / fun, to an extend that most 384 bonuses were stronger than the 391 heroic ones from firelands. On top of that they made a couple of OP trinkets that's are a must have for most players, again 384 often oughtweighs the 391's.

That made that a lot of seasoned raiders had to run LFR on their main for weeks/months, to help progressing the main raid. Which was the goal of Blizzard, because if you make a group only consisting of the average LFR skill, they won't get past trash. On top of that the seasoned raiders who were forced to run LFR often brought friends along to help roll on the items. <insert big random number>% of the LFR got boosted by them; they had to shut up cause they clearly saw they got outperformed by miles.

After so many months they finally master the mechanics of dead simple encounters, and the seasoned raiders have no more reason to join LFR (unless on an alt alt); which basically makes those kids cocky again. The spout their nonsense all they long, standing in fire and doing silly dps.

I know I generalize and exaggerate a bit, but you get the picture.