While I haven't looked at any extensive statistics, so correct me if I'm wrong, but feral tank population was behind the other 3 tanks in LK as well. So, the population not being down from LK levels doesn't mean that bears aren't the least common tanks.
As for why there are few bear tanks, all reasons are pure speculation with little evidence to support them. However, I do think that the sorry state of low level bear tanking does directly lead to fewer bear tanks at end game. If someone in your guild tells you they want to roll a tank, and asks for advice on which class to level for tanking, do you recommend levelling as a bear tank? I know that I'm pretty honest about it, don't level as a bear tank, the lack of abilities will prove endlessly frustrating, level as a dps or heals. I actually think the biggest problem with low level bear tanking is not Swipes cd and not being available until 36, I think the problem is Lacerate still not being available until 66. Not having a spammable attack until 66 leaves far too many gcd gaps in the rotation, this, combined with the Swipe CD makes tanking pack of mobs incredibly frustrating, since tab targetting single attacks is only a barely viable option.
It's a fair point that valor point gear isn't all that good for bear tanks. I'll admit to not having looked real closely at the itemization on a lot of the pieces, having long concluded that the 2 piece set bonus is worthless for tanking, meaning I almost certainly wouldn't bother going for the 4 piece.
Yes, my gear is reforged for hit and expertise, and yes, I am running a dps trinket. I tank almost exclusively heroic 5 mans. Since healers have almost no difficulty keeping me up, stacking dodge wasn't proving to be of significant benefit, and getting hit and expertise has made my job that much easier. If I'm tnaking a raid, its easy enough to take 5 minutes to reforge all my gear and swap a trinket.
I do have a question, why do people rate the Bedrock Talisman so badly as a tank trinket? How much physical damage reduction does 1200 armor provide? The dodge boost below 35% health certainly seems a pretty decent proc for a bear tank, at least for fights where the vast magority of the damage is physical. Certainly in a magic damage heavy fight, the trinkets value is really low, but I'm confused as to why people find it to be worthless when looking at it from a physical damage mitigation perspective.