They're generally licensed with CC-NC-BY plus no derivatives (akin to GPL), but I don't want my images to be taken to a training set to feed a generative model without my consent, because you're violating the license terms I put on it.
Same is valid for my code. I stopped using GitHub, because it devours any and all open repositories regardless of its license and without asking for consent.
This is not about scarcity, but respect and ethics mostly. At least, from my perspective.