I haven't used Kagi much, but I don't think I've ever seen a single Pinterest result from any other search engine, I barely even know what the thing is for.
Maybe you just don't really search for images? Pinterest constantly comes up in image search results and then doesn't actually let you view or download the full image until you sign up.
And to be honest, I don't see as much Pintrest crap as I used to. It may just be that it has fallen out of favour because of its terrible design. But it was a site that basically let you create mood boards from images that you found as your browsed.
The big problem with it was that it simply copied the image so if you were looking for anything, Pintrest came up with the images for a product but then had removed all the source so it just flooded search results with uncited references and you couldn't find anything useful.
Reverse image searching to find sites thst sold a prpduct became useless.
Possibly a US thing, definitely not a Kagi thing. Useless Pintrest results (especially in image search) that don't actually the thing they pretend to are ubiquitous on Google.
Unsurprisingly it's Pintrest that annoys people the most.