Because there is simply no need to.
If there was one significantly better overall than Google (and not just a little better or better in just certain niches) people would switch.
Even if the products are better people don’t switch. Google organic has been a spam cesspool for a while with a few layers on top of ads and people don’t switch. I know some people that use Bing because it is the default of windows and they don’t switch.
I've used bing for a decent while but since they can't make a normal website that works on Firefox their slightly inferior results made me use Google again.
