I think high profile sites are better served by static pinning, which seems simpler to maintain and also comes with the benefit of preloading. Thus, if you have

I think high profile sites are better served by static pinning, which seems simpler to maintain and also comes with the benefit of preloading. Thus, if you have those sites at one end, and lots of small/no-large-risk sites who don't need any pinning on the other end, you're left with no one for HPKP to serve in the middle. But, if HPKP were easier to deploy, perhaps more sites would use it.