In my opinion, everyone who's willing to pay for a good IDE is already subscribed to JetBrains. And since they have static analysis, excellent refactoring, and plenty of navigation aids for foreign source code, I never got frustrated enough to start DuckDuck-ing for another external tool that might help.

Accordingly, I believe that new developer tools are difficult to monetize because the established ones are already exceptionally good. There's no customer pain to alleviate.