This is so misleading that it hurts. A user is not a user! How can you compare users of sites that create content (e.g. Geocities, Youtube) to users of sites that write comments on content (e.g. HuffPost) to users of chat programs?
Because for social media company, so much of their value is derived from the size of their user base. Obviously number of users ALONE isn't enough, but it can be used to prove an interesting point; that even though WhatsApp / Instagram seemed ridiculous, they paid way less per user than other companies did back in the day. This is very interesting
