You oughta open a FB quarterly presentation some day, it is quite eye opening how off the charts they are in terms of user monetization. $20 yearly wouldn't cut it at all, in North America the average revenue per user (ARPU, trailing 12-months) is about $145 (yes, $145 * 253M monthly active users). It's not even enough to match the worldwide ARPU (about $29, for 2.6B users). The value FB extracts from it's users, particularly in NA, is simply astonishing, I'll leave you to Googling the ARPU of other web platforms to get an idea.

https://investor.fb.com/financials/?section=quarterlyearning...