why do we earn lots of money from Facebook in comparison to Youtube?

Because Facebook viral videos within 24 h of new pages and Youtube did not have viral videos of every new channel.

Why Facebook

People use Facebook more than that youtube. That's why Facebook viral the video with is 24 h and makes the person a celebrity with is 24 hours. Facebook is a very big platform for every person who wants to make money from Facebook. 

Facebook Earning Rates 

Facebook videos get views in millions and engage a very large amount of audience. this is the best way to earn more than that youtube. Youtube gives a large number of earnings but in the comparison to Facebook, these are a little amount.