The problem is Joe Billy who buys a random phone (who is also 90% of the marketplace) does not care at all if the applications he is using are made with HTML5/CSS/JS, Lua, C#, C++, C Triangle, Delphi, Dolphin, Chicken Horse, what ever. All they care about is...
1. Does it work.
2. Does it work well (ie fast, do what it is suppose to do).
3. Does it not cost anything (or if it does cost anything, an amount which is appropriate).
4. Do his friends have it.
That's really all they care about. At the end of the day, nobody cares if it's Firefox OS, Android, iPhone. So long as they can do what they want to do at a cost they can afford. Their friends have a similar device or allow transplatform communication. And they can get all them fancy stuff their friends show them (ie amazing apps, themes, custom phone skins, etc).
The people who care about the other stuff don't make up most of the market.
And that is something Microsoft as well as Google, and Apple get. The goal is to have a cool phone, with stuff that is cool, at a cool price. That's why people like Microsoft pay app developers to port their "cool apps" to MS App Store. As well as give "celebrities" free phones. All in the name of coolness!