It's simple really. Advertising sells phones and MS doesn't advertise. No electronics manufacturer advertises more than Apple, and their ads are effective. They are simple and they actually SHOW WHAT YOU CAN DO WITH THE PHONE. Compare Apple's ads to the crappy commercials MS came out with last year which barely showed the phone at all. The WP7 strengths are the live tiles and the deep integration beween apps and the UI, which will be even better when Mango is released. MS needs to highlight these advantages in simple commercials which show how these attributes will make your life better. For example, the press of a single icon for 'local search' with Mango as opposed to opening several separate programs on a iphone or android device to get the same information. Don't be cute and don't be mysterious (did MS learn nothing from Palm's WebOS disasterous ads and subsequent failure).
MS also suffers from the fact that they are MS, the evil empire, while Apple and Google are cutting edge and cool. Does anyone doubt that if Apple had developed the Metro UI it would have been hailed by the blogsphere as the most advanced, groundbreaking, thinking-outside-the-box, this-will-change-your-life-as-you-know-it piece of technology showing just how far Apple is ahead of the competition. Most of the tech blogs dismiss WP7 because it isn't Apple and it isn't Google, constantly focussing on what's lacking and not what it can do.