- They found the internet had gotten a new icon and had no idea how it got there. (bundling with popular software)
- They were instructed by google.
That is how chrome came to top. See other comments for more context.
The fact is, browsers aren't a product, they're a platform feature. Users have zero incentive to ever switch from whatever their OS came bundled with, unless you make a massive advertising push. The fact that Google managed to get people to switch to a non-platform browser at all is a shocking achievement.
Would you rather everyone still be using IE? Because that's exactly what would have happened otherwise.