I already copy boilerplate code verbatim from docs or stackoverflow.

That code has predictable license terms. You have no idea what the license terms are for some random code that an AI plagiarized for you, because you have no idea where it even came from.

Also how would that work in closed source programs?

I don’t know, but Stac Electronics somehow figured out that Microsoft plagiarized their code, so it seems best to assume that I will also be caught.