"In the M365 apps, we do not use customer data to train LLMs. This setting only enables features requiring internet access like co-authoring a document." -@Microsoft365
They wouldn't have to combat misinformation if they actually told users what the switches turned on/off instead of vague descriptions that could plausibly allow them to do whatever the hell they want.
I'd imagine mostly to the productivity of the sloppers. Considering this looks like a Windows Office-wide default opt-in, I feel you'd have difficulty hitting 1% userbase.