Google not planning to "build out Windows apps" because the users aren't there
Google has not been quick to support Windows Phone so far, only putting out one official Google Search app, which obviously didn't have much time or energy put behind it. And, it looks like Google isn't planning to work any harder to support Windows 8 or Windows RT either. According to Google Apps product management director Clay Bavor, Google is not planning to "build out Windows apps" because the users just aren't there.
Google has made a Google Search app for the new Windows Modern UI, and it has added support for the Modern UI in Google Chrome, but apparently the company doesn't plan much more than that, preferring to point users to the web apps for Google products. Bavor went on to say, "we are very careful about where we invest and will go where the users are but they are not on Windows Phone or Windows 8."
Of course, Bavor left open the option to reevaluate this position if things change, but for now the company will continue to focus on Android and iOS development.