There are some interesting statistics about biography reading in public libraries in the Library Journal article "Materials Shift/Materials Survey 2014" by Barbara Hoffert. In circulation of nonfiction books, libraries responding to the survey put biography now at third highest category, after cooking and health/medicine titles. On the nonfiction ebook downloads chart, biography is in first place.
There is more good news about the circulation of library materials in the article. It is worth reading.