Yes, but one eventually faces the need to update the certificate on the server, and still support installed applications (which fails when apps have an obsolete certificate pinned). Hence the need for smooth certificate updates, and the good smell of HPKP. But it addresses another need, hence my confusion.
Mobile apps typically have other key pinning mechanisms that are preloaded (i.e. baked into the binary), but that's typically easy to bypass if you're the owner of a device; it's not really effective as a mechanism against reverse engineering.
Your comment makes me realize that HPKP can bootstrap itself, and is unlike regular pinning (with certificate bundled in the binary, as you say).
So do you agree that a powerful enough owner of the device should be considered able to setup a server which poses as the regular server the app talks to, and sniff any request the app sends to its server?
(edited for spelling)
I think any attempt to prevent that is doomed to fail, similarly to how DRM has had absolutely no effect on the availability of pirated content.
HPKP's only purpose is to protect against malicious or compromised CAs.