Why don’t people build mobile sites?

Over the years as I’ve spent more time on my cell phone for data access (markedly more since I got a company phone), I’ve wondered why more websites don’t have a mobile version. Of course there are a few big companies that have mobile versions (like Google) that are basically as good as their regular site (granted Google’s regular website isn’t terribly complex). Some companies (such as Starbucks) have mobile...