I'm guessing that the "marketplace" and "sale" refers to sites like "Mage Space" which charge money per image generated or offer subscriptions. The article mentions that the model trainers also received a percentage of earnings off of the paid renderings using their models.

Obviously you could run these models on your own, but my guess is that the crux of the article is about monetizing the work, rather than just training your own models and sharing the checkpoints.

The article is somewhat interesting as it covers the topic from an outsider's perspective more geared towards how monetization infests open sharing, but yeah the headline is kinda clickbait.