I suppose the same reason why qwerty still reigns supreme despite being a purposefully inefficient layout, people know it.

On a similar note I was talking to someone recently about touch screen phone keyboards, and how compressing a qwerty keyboard onto a (relative to the size of actual keyboards) tiny screen with very little haptic feedback seemed like an awful idea that was used early on because it was easy to understand and since then we've just kind of stuck with for no reason. The person I was talking to agreed, and we were thinking of ideas of how it could be improved. Later I was talking to a my two brothers about it, who are more a bit more normal, and neither of them thought it was worth the effort at all (and they're probably right), and thought it was pretty daft thing to care about.

Long story short, if it aint broke, don't fix it I suppose