I don't know about the NIH specifically but often what happens is journals will charge to make/allow an to be article open access. The NIH will give/include in

I don't know about the NIH specifically but often what happens is journals will charge to make/allow an to be article open access. The NIH will give/include in grants funds for paying journals to make a paper open access (often a few thousand USD). So in some ways the journals don't care, because they're getting paid. Personally, I don't like an author pays model much either, as it doesn't account for scientists working outside their grants (or God forbid independent scientists).