Well, I wanted something with structured records. `pass` can sort of do that, but it's not built into it.
I also wanted to take advantage of KBFS to do the encryption transparently and expose records as individual files. KBSecret just provides a structure; you can use plain old shell scripts (and I/O primitives) to access your records once they're in place.
It's more of an experiment than anything else currently, but those are the two big motivating ideas.
The original pass program allows overriding the default directory with the PASSWORD_STORE_DIR environment variable. I use gopass [0] though which supports directly configuring this via cli/config file.