Re: "but could for example, also be done through ads on a trusted website"
That's exactly the reason. It's even - gasp! - irony. Like "they couldn't care less" so much that they couldn't be bothered with the "-n't".
People criticising slang idioms in different versions of English is tedious in the extreme. FWIW, Americans use both, and there are plenty of Americans who also criticise the "could care less" version among their own. Again, slang, who cares?
If you see it in formal writing, sure, get up on your hind legs then (but make sure it's not a perfectly acceptable variation in their English first).