It doesn’t come up because the impact is minimal. There’s no likelihood of confusion that it’s an authorized licensure and no one is making money on it. People who make money using their likeness know - assuming they know or care that online RP exists - that it does not cost them anything for their face to be used in this fashion because it is not an area of business that it would earn them any money. Essentially, is it morally correct to “steal” someone’s face for this purpose? Probably not, but also who cares? What harm exists here?
Basically if you want to use AI PBs go ahead, but this idea that it is somehow morally superior because no real people are involved is disingenuous. The only choices that are free of contention are drawing your own shit, paying to commission an artist to draw your own shit, or not using an image at all and just writing descriptions in this writing hobby. Otherwise we are all making choices that have points of compromise.