This seems like a know your audience situation.

>However, in a world of commodity AI models, can simply use a model from an AI provider that does not watermark. Or download any open source model and run it themselves

That's seems above the skill of the majority of the population that might be tempted at using generative text. I'm thinking of students trying to "write" a paper, or any of the myriad of other things people are blissfully unaware of how genAI works that are using it every day. For those people, that just use the default prompt to blindly copy/paste away. For techy nerd types running from CLI, yeah, they could simply use a different model.