Your prompts, especially if they contain your entire codebase, are _way_ more data-rich than an airline phone call or 1920's novel. So they _are_ going to train on them, no matter how many checkboxes you tick to stop them. Which is both a commercial risk and a massive new attack surface.
It's not just software developers; if law firms aren't controlling any public LLM prompts _very_ carefully, they can expect some meaty client confidentiality suits. In fact any organisation in a competitive environment should be worried: Acme Bolts: "Write me a presentation for Zoom Construction". Beta Bolts: "Is Acme Bolts pitching to Zoom Construction?"
Maybe this is part of why OpenAI and Anthropic are finding demand softer than they would like. And why open-weight models that organisations can run on exclusive hardware are thriving.