I can't speak for everyone, but to me the most accurate answer is that I'm role-playing, because it just flows better.
In the back of my head I know the chatbot is trained on conversations and I want it to reflect a professional and clear tone.
But I usually keep it more simple in most cases. Your example:
> I'd like to add email support to this bot. Let's think through how we would do this.
I would likely write as:
> if i wanted to add email support, how would you go about it
or
> concise steps/plan to add email support, kiss
But when I'm in a brainstorm/search/rubber-duck mode, then I write more as if it was a real conversation.
I agree, it's just easier to write requirements and refine things as if writing with a human. I no longer care that it risks anthropomorphising it, as that fight has long been lost. I prefer to focus on remembering it doesn't actually think/reason than not being polite to it.
Keeping everything generally "human readable" also the advantage of it being easier for me to review later if needed.