because many people (including me) don't trust google. Also, it supports different things (yes, technically more overall, but still different things) than other browsers. In addition, Chrome is less secure in some ways than other browsers. It allows anyone to easily mess up your printer, because it includes Cloud Print, and it has other security issues. It may have been the first bug fixed, but in the recent browser hacking competition, Chrome was the first browser to be exploited. And it was easy.
Also, people are stupid and they don't like change. Maybe that account for a significant amount of it.