This may be a cause for a lack of voices, but it's hardly the only (or I'd argue even the most prevalent) cause. 99.9% of the developers at the company I work for are on macbook pros, yet they only support Chrome. And the reason is simple: they don't want to support more than the one browser.
The decision was, of course, backed up by numbers, harvested after our product's use of Chrome-only features and "best on Chrome" style "help" answers.
It's a self-reinforcing loop.