People who leave a service when the terms change in a way that negatively impacts their privacy are clearly choosing based on privacy reasons though (mostly anyway, some might be leaving because their friends left).
Except that the terms of service didn't change in a way that negatively impacted their privacy - they were taken in by misinformation that was left to spread unchallenged because the mainstream media had an axe to grind against Facebook. The net impact of which is that their conversations are now less private and they don't even realise it.
Beware of the malicious PR campaign carried out by Facebook. The terms did change in a negative way, it’s enough to read them to see it. Even for EU users. Later, when Facebook realized this time things would not be ignored, they started their PR campaign. First the claimed that in EU there would be no changes, then (first time I see it in the linked article) they claimed that there were no changes anywhere in the world. At the end of the day what matters is what is in the terms, not what the spokesperson claims. And in the terms there is no opt-out from sharing data with Facebook.
The terms did not change in a malicous way, because they were already malicious. There never was an opt-out of sharing data with Facebook:
> Specifically, users had 30 days after first seeing the 2016 privacy policy notice to opt out of “shar[ing] my WhatsApp account information with Facebook to improve my Facebook ads and product experiences.” The emphasis is ours; it meant that WhatsApp users were able to opt out of seeing visible changes to Facebook ads or Facebook friend recommendations, but could not opt out of the data collection and sharing itself.
