When we first deployed our policy there was no support for reporting in browsers. I think that Firefox still lacks support and chrome only added support recently (I'd have to double check, or I'm sure Scott knows).
Exactly right. The only browser that will send HPKP reports right now is Chrome and that was very recent.
No, but that doesn't impact the operation of enforcing the use of their public keys which is the main purpose. It's definitely preferable to have reporting though.