Things are changing rapidly in the publishing business. It used to be a person would write a book--perhaps based on her established platform--and then her agent would frantically look for an audience to sell to. Another way to write is to know what a niche is looking for and to write specifically to them, for them. The difference in writing is one is writer-centric the other is reader-centric.
Since we live in a day where personal value, take-away and "what's in it for me" attitudes prevail, giving your readers what they're looking for is important. Otherwise all you're doing is spouting, pontificating, reporting or commenting on something they may or may not care about.