Most people run 7 because not because they wanted to (they skipped Vista) but they were forced to by XP's end of life.
I imagine man users didn't know what to expect. Microsoft has the worst advertising and promotion I can think of. For instance why would people in the market for a tablet buy a Surface? All they've seen in the advertisements is hipster morons dancing on a table in a confrence room. No product knowledge in the advert.
Apple runs an assortment of campaigns. Some inform, others are touchy-feely. The best ones put the camera right on the device and quickly demonstrate the ease of use of a single app or function. Even the Mac vs/ PC ads usually conveyed something useful.
Now Google is in the consumer hardware market with the Nexus tablets and Chromebooks. The tablets are amoung the best in class. the Chromebooks are inexpensive and an attractive alternatives to MS and PC laptops. If you're not a gamer and just want bread and butter features it's a big savings.
MS under Ballmer doesn't compete. They expect you to care enough to inform yourself. The market shows most people do not.