Main reason being they can't even compete on price without those fat carrier subsidies that it took to get Android for phones off the ground. They're pretty much at price parity with the market leader with a fraction of the useful apps, and surprised why they're not selling that well.
Anyone who thinks Android would be the leading smartphone OS if their devices were sold at price parity with iPhones is deluding themselves.
Similarly, if Apple wanted to overtake Windows PC markethsare with Macs (they don't) they would be foolish not to compete on price. When you are asking the user to try something new (or new to them) and non-mainstream, "pay more for this risky new thing" isn't a very attractive proposition.
I would like to see where that number is coming from. I've seen a lot of number's based on units shipped, but none on "actual" units sold. Curious what the 20% is actually based on.