Does History Sell?

At a recent gathering of writers from around the country, I talked to more than a few bemoaning the difficulty in selling non-fiction on historical topics. One reported being told by an editor, "Well, we have Russell Freedman."
    Another editorial comment, "It's so labor intensive. We just can't take on very many projects."
    Biographer Brandon Marie Miller believes we're in a golden age of history books for kids. She says, "Books are more inclusive of peoples and cultures. They have lovely illustrations, photographs and prints. Many have maps, sidebars and helpful back matter—time lines, glossaries, places to visit, bibliographies and source notes."
   Brandon writes for Chicago Review Press. "I've proposed my own ideas for all my books—although I've had an "in" with editors I've already worked with and I was able to bounce ideas off of them before submitting a written proposal or outline for the selection process."
  I'd be interested in hearing from others writing history for kids. How do you see the market?  What factors most influence the whether an book proposal on a historical subject will sell?