It's not always necessary to compensate those whose labor helped you. I haven't compensated many of the open source projects I use, for example, even those who clearly want me to (with nagging pop-ups). If the use of copyrightable material to train a model is legal, and it does not legally require compensation, it might be difficult to argue that the use of such material should be compensated or else. It would depend IMO on whether there are norms in place for this kind of thing, and I don't necessarily see wide agreement.