And why have I heard absolutely nothing about it, anywhere?
"All RAW is these days is a cheap version of Saturday Night Live, so if you wanna tune in to watch the amazing star power of Al Sharpton and Nancy O'Dell, go ahead! Who's gonna host next week, Big Bird? Wow, that's must-see TV!" - John Morrison (10/16/09 Smackdown!)
Dunno. Wikipedia says they had four left over (the last episode of the season was the last episode of the series, and these four would have fit in right before that last one), and they're airing in syndication (not FOX - although your local FOX station may have the syndication rights) this week. I suspect Adult Swim will eventually get a crack at them as well. My own personal excuse is I don't watch my local TV station enough to see "King of the Hill" ads.
They're not "new" per se. The made them years ago, but never aired them. They've been floating around on the internet for some time, and I think they're included on the DVD sets, but I'm not sure about that.