Searx and Searxng existed side by side for a long time. Searx had a focus on privacy without compromising, Searxng has a focus on usability. So Searxng uses javascript, works better on mobile, and does things like search suggestions.

I think there was a disagreement on direction of the project so it was forked and both versions were maintained until now when they are reasonable different from each other and the original is falling behind in features and updates.