Because numbers dont lie, and following numbers, "Basically no one" raided outside LFR, which is why it was introduced, and when that number reaches 50-60% active players on WoW active periods (aka expansion launch), you understand how its different.
Its the same reasoning with Naxx in WOTLK, only 10.000 people entered Naxx in Vanilla or so, and the game had already hit like 7-8mil players by then.
People dont seem to understand that yes, maybe 100K-200K (example number) players were raiding in early Cata, the rest 11.8mil reported active players?