Ecosia already has more users than Brave Search according to the few sources I could find that even tried to estimate market share for search engines that niche. They’re all less than a percent either way though, and nobody’s gunning to beat the 13th most popular search engine, especially when number 1 has 80-90% of the market according to most estimates.
I think you’re confusing privacy and security. Some of us aren’t really worried about the NSA hacking our phones. We would just like for it to not constantly be selling out every minute detail of our personal information to a mega-corporation. Sure, you still have to pay attention to what apps you install and all of that, but a de-googled android phone is still a massive upgrade in terms of privacy even if it isn’t super secure, as long as you aren’t being individually targeted for some reason.