That's a terrible analogy. Are you saying that once a visitor completes a captcha on your website, they can steal all your stuff? In that case, the problem is with you and your website security.
Well, a more apt one would be that someone breaks into your house or car and puts all their litter everywhere so that you have to spend hours or days cleaning.
Sometimes I don't get the logic of these spambot creators. Do they honestly believe that creating thousands of fake accounts with links to "hot dating site" in my webshop will help them in any way? These data are completely invisible outside (why would anyone want to present their customer data to the world).
wow, this actually happened to a coworker. He waked up one day discovering a broken window and human excrement everywhere.
For sure he closes everything now.
The goal is link building[1].
I don't think they actually expect the links to be published, so much as they expect the webmaster to read them in their moderation panel.