You're the one who's wrong. CC-ing mobs at the start of Cata was a thing. I can wager a guess why you don't remember, but I'll give you a sort of proof instead. There was a change that should be in the release notes where CC changed the way it worked in the initial weeks of Cata. The change was made so mobs didn't pull mobs when placed (a change that survived to this day).
You think Blizz decided all of a sudden to change this when people didn't CC at all?
I'll do the rundown of what happened at the start of Cata:
- some people moaned loudly (as per usual) how boring Wrath dungeons are; how awesome BC ones were when you needed to CC and shit and actually worry about aggro;
- obviously, these people were thinking of the end of the expansion Wrath dungeons where we had jokes running around that it's enough to put down consecration and go afk and you'd still hold mobs and never die (obviously, we were overgearing them by miles)
- but Blizz made the Cata dungeons feel more like the BC ones anyway; they now required 2 things:
1. CC
2. Interrupts (whoa, what's an interrupt!)
They also lowered aggro by a lot, bosses required actually doing some mechanics (like kiting, dispelling, priority killing etc)
- A decent coordinated group was having a lot of fun - we marked targets (whoa... marking!), we coordinated CCs - CCs had to land at the same time and the tank had to be ready to take them without breaking the CC; this was FUN; As a paladin, I could pull from range and my shield didn't break CC - which meant I was pulling them safely so dpses wouldn't break CC either
- But then you had the other people: people who didn't know how to deal with changes; useless tanks who tried to pull like in Wrath or those who broke CC and didn't understand; dpses who didn't know about CC or just wanted to dps like in wrath; for the majority, interrupts didn't exist; so basically pugs, especially those put from LFD had MASSIVE issues completing the dungeons (so yeah, a lot of ppl don't recall CC because they were NOT CC-ing, they were just wiping and going again)
- Tanks stopped tanking, it wasn't fun for those who were only doing it in LFD and weren't dedicated; numbers dropped; people at the start wanted to level in dps anyway, so obviously you'd have less tanks anyway; even holding aggro was bad because you needed expertise and hit not to miss or be parried;
- I recall people crying they weren't able to do their daily dungeon in an entire day; and it was needed because you were getting VP and those red orbs for crafting
- And here's the thing, people were whispering me offering gold to tank for them all day long - so yeah, paying a tank to tank isn't a new thing, it's always been a thing for when you just can't get a bloody decent tank
- So... Blizz changed stuff; they nerfed the dungeons HARD twice in the beginning few weeks; they changed the CC so it wouldn't engage mobs; they gave all tanks interrupts so they wouldn't rely on crappy dpses; aaaand... it was still kind of an issue with tanks, though not as bad as before
- People started getting more gear (and raid gear), some people who were displeased just quit (there was this massive drop, like 2 mil people at the start of Cata) and so the issue lessened
- Blizz added call to arms here I think, rewarding tanks for participating into LFD alone; and tanks were still pretty scarce; so eventually they changed the aggro modifier to 5x halfway through Firelands and all of a sudden there were tanks. Tanks all over once again.
So to actually be on topic, there's a lot of things that help with tanks: tools, self sufficiency, LFD (yeah, hate it, but people who couldn't get a tank were getting one, even if a shit one), but the ONE thing that adds more tanks to the pool is THREAT. Because those tanks that are added aren't your dedicated ones - those will probably stick with their guild groups and not bother with random. No, you add those who don't enjoy the challenge of threat or being responsible for their group's mistakes. Which is the majority of tanks.