I think it's just a misunderstanding. People need to look up the meanings of terms like royalty free if they don't understand. It's all there on the sellers' website, along with the price of a licence.

Your plan to create your own works is a good one, but you can't beat just taking your own photos. I do that mostly. The artists aren't paid for their images being used by AI, and they've not given permission. That's why there's currently a law suit in action about that too. https://medium.com/illumination/lawsuits-for-ai-generated-imagery-have-begun-bb8eb6394bd0