You have to be rather naive if you don't think these companies don't simply train on your prompts with or without your consent. They literally scrape everything - legal or not - and claim its fair use to train on, including straight piracy The idea that they'll steal from everyone except you is just wishful thinking
(To put it another way: if the copyright arguments against training on data scraped from the internet fail, the big AI companies don't really have a business, so they are going to proceed on the basis that they do until someone forces the issue otherwise. They don't need to train on data from their customers, and that is an argument that is almost certain to fail in court. If you're carrying 100kg of cocaine in your car, speeding is a really dumb idea, but the analogous action here would be firing a machine gun into the air from the driver's seat)