I believe that when the call center is busy, the overflow calls go to a 3rd party company, and you're right, they don't really know Disney or the Fort at all.
But that being said, you can get "local" cast members who don't know anything about FW. You'd be surprised by how many have never even set foot on FW grounds. I was a reservations CM at the end of the last century (it feels weird to say that) and most CMs were very intimidated by guest calls for FW. They didn't know the difference between the site categories or the amenities available there. They didn't know what a full hookup was. I had other CMs coming to me regularly for help in understanding FW.
I think it would be great if WDW started a FW only call line, like you call the regular number but then have an option to select a FW reservations CM to speak with. I would go back to work for Disney if they did that.