The journals don't really care about preprints. Most of their revenue comes from university subscriptions, and so long as they can claim that their paywalled ve

The journals don't really care about preprints. Most of their revenue comes from university subscriptions, and so long as they can claim that their paywalled versions of the papers are the final and official ones and the preprints are merely unedited drafts, there is no threat to that revenue stream. (Placating the journals is part of the reason why they're called preprints rather than just papers. On Arxiv, authors will often update their preprint even after the paper is accepted in a journal.)