There are no technological or commercial barriers to switching search engines: no-one is making people use Google search (except I guess maybe on Android devices or Chromebooks -- I don't have and have never used either, so I don't know).
People use it because either (a) it returns better results or (b) inertia.
If it's (a), using it is a rational choice (though one that could be trumped by privacy or ethical concerns).
If it's (b), eventually they'll be knocked off their perch by a better search engine.