> My wife is a mystery fanatic and she wonders why Piper didn't pursue
> more mysteries. She rates Murder.... right up there with Agatha
> Christie. From her that is high praise.

I agree with your wife.

But Off the top of my head, I don't recall how well Murder was recieved
or performed over the long term

Most of Piper's world building and ideas about the flow of history would
have to be put aside.

Murder mysteries are about people. You have to do people building the
way you do world building.  And many of the people are broken in amusing
or depressing ways.

Might be a world that HBP didn't feel comfortable living in.