Everyone is used to going to Google to search. Heck, you often hear people use the word google instead of search. This habit is hard to break. Switching to the competitor is not just a few keystrokes away. It takes breaking the habit of reaching for Google whenever I need to search.
It takes more than a slightly better product for folks to break this kind of habit. It's the same reason why Google has trouble competing with established search engines in other countries, even if Google has better results.
When Google came out it was a LOT better than everyone else, so people switched. Now the competitors are barely catching up to Google, or at best making incremental advances over Google: not enough to get people to switch.