A previous thread on the topic: Will Mojeek Offer a Premium Service to Searchers?
Much like browsers, people have been trained over many decades not to pay for search engines. When your competitors are giving away their service for free, it’s a hard market to break into. Building a search engine is really hard already, so even Kagi, which does offer only a paid service, is ultimately leveraging other search engines like Google and Mojeek to deliver it.
Brave Search has the option to pay not to see ads, and has their own index. That’s about as close as you’ll get today.