A lot of open source software is made by enthusiasts for free. A lot more of it is made by companies like Microsoft or Google for various reasons - I believe mostly to claim “we’re open source”, but also to entice others to contribute more code that they can leverage for free, which is a valid reason too. One thing is sure: they do pay their engineers’ salaries
Free services however… That’s different: we all know why Microsoft or Google propose free services.
Now this unknown search engine you linked to: they could be funded by idealists who want to promote privacy, like the Calyx institute for example. However, looking at their website, I see no obvious reason why they propose the service they propose: they do have a Donate button that leads to a page with 4 payment links - 3 of which crypto - and their About Us button leads to a page that just says “test”. Kinda sketchy…
Therefore, I assume it’s up to no good, because that’s the reasonable thing to assume with any unknown website that looks sketchy.