They don't release paid apps on Android because it's not their business model to charge for apps; they don't even charge for Android itself. But they do release

They don't release paid apps on Android because it's not their business model to charge for apps; they don't even charge for Android itself. But they do release pretty serious apps, see recently Chrome for Android. Google pretty much do the other way around: they build tools they need for their own developments (Closure Library, v8, Go...) then release it Open Source for others to use.