Situation is much different now. Most Internet users don't even know what's a search engine. They just type in the URL bar and the search is performed transparently. Google has majority share on two main platforms (Google Chrome on desktop and Android on mobile) ensuring that their search is the default for the majority of users and is something people would get used to.
If a user isn't aware that choice even exists, they have no choice.
I believe this was recognized by Google years ago and thus their move into Android and replacing Firefox. Looking back, those were really smart, well executed strategies.
Even if Google search were to drop quality, it's so entrenched that it would take enormous effort to replace it at #1 spot. You would have to build a mobile operating system, a browser and a search engine - and all three would have to better in some way for users to switch.