Kagi founder here. This is very early (alpha) concept built by a single Kagi Labs developer in a few weeks. The proper infrastruture and product is not built yet. We are launching a prototype to get feedback and gauge demand.
Why does this exist?
It would be an efficient way for us to build and expand our own index. Assuming users of this would be Kagi users, we would expand our index by tens of thousands of high quality? personal websites, hobby projects, startups, documentation websites, etc., also helping to surface them in our results (where relevant, like we already do with Kagi Small Web initiative [1]). It is a win-win for both our users and Kagi.
It would also be a way for Kagi to get some exposure outside of kagi.com (provided the search widget has some branding on it).
This is why it makes sense to offer it for free for smaller sites/projects.
And crowdsourcing index is completely opposite direction of one that causes deterioration of web search results in ad-supported search where few entities control the majority of space [2], so we like it.
That is the plan - and since this is a "Labs" project, we are open to it crashing and burning. Know we do not, until we try. Try and try again, we must.
[1] https://kagi.com/smallweb
[2] https://detailed.com/google-control/