So... based on nothing you're making these assumptions. Despite the fact that there was no increase in bosses this xpac (in fact there was a 13 boss decrease from last xpac), despite the fact that there were only 2 tiers this entire xpac(the least in wows history)... meaning only 2 sets worth of tier etc which is one of the biggest resource hogs, and despite the fact that people complained excessively about tuning and mechanical difficulty issues in normal / heroic... they put more focus / resources into raiding this xpac.
Right.
- - - Updated - - -
They pop up and usually almost instantaneously fill.
They're not unheard of, they just don't spend anywhere near the same amount of time filling up as the groups that have ridiculous requirements. Which means they're nowhere near as visible as those groups because if you weren't there for the small window where they were up then you didn't see them.
I'm not really sure why blizzard keeps the aotc achievement for normal / heroic when they full well know that its only real purpose at this point is to cause bad player behavior.