I don't think the service needs to be critical for it to be an "outage". If the service is unavailable to people who use it that's an "outage".

You could have a soft-serve ice cream machine outage.

Of course they do. In many developing countries, Facebook IS the Internet.

https://qz.com/333313/milliions-of-facebook-users-have-no-id...

I hope not.

But in some countries many small to medium businesses use WhatsApp extensively for communication with their customers. For many people it's as bad, arguably worse, than their main ISP going down.