Because whatever you send to ChatGPT may be future training data for their AI model. Mixing up your data with other customer's data is not really part of Slack's business (yet?).
> When you use our non-API consumer services ChatGPT or DALL-E, we may use the data you provide us to improve our models. You can switch off training in ChatGPT settings (under Data Controls) to turn off training for any conversations created while training is disabled or you can submit this form. Once you opt out, new conversations will not be used to train our models.
