More than half of that 10-12k is lvling, and people don't do bgs as much while lvling.
And again, how can you link that to crossrealm? If the realm is pve oriented and most only pvp casually now and then. What proof is there? none. You'd have to disable it for a few months and check after, which I doubt will happen.
People are doing raids, are afking in dalaran, are llving. I mean I had people with 4.5k gs doing 2.2k dps in a rdf hc, do you think that kind of player would fare well in any pvp scenario? xD
I didn't say that Lordaeron pvp is ACTIVE because it never really was once Icecrown got out and people started transfering- except peak hours-, but with crossrealm you can have a bg at any point during the day without much waiting and that is the point of the feature. People on Lordaeron simply don't pvp as much, or not in bgs/arenas, they seem to prefer brawls in open world.
You can't really blame a feature for the nature of the realm. The players that were into pvp left, they ain't coming back and they weren't many to begin with. Crossrealm ensures that if you wanna pvp, you can at all points in time.
Get your gear and go. Is it harder? YES. Is it impossible? NO. That's my point