My experience was that IE finally got bad enough (around version 8), and Chrome got good enough, that even "grandmothers" started having everyone telling them to use Chrome, and it was so incredibly superior that you didn't have to be technical to appreciate it.

Now the reason everyone uses it is because it's psychologically the new "default", whether it is on the actual system or not. Everybody knows that's just what you do when you get a new computer: you go install Chrome. And the irony is that even now, with Edge being basically the same thing, most people don't bother to re-evaluate that default assumption that "the windows browser is bad". They just use Chrome.