Why is Facebook's revenue so low than Google's

So y do i think facebook can not match google any time soon atleast in terms of revenue?

There is no doubt in anyones mind that facebook is at the top when looking at the amount of time ppl spend on a website.. there revenue is still 1/8th of what google does.. So, the challenge with facebook is not getting people on their website but to put ads which are more relevant, so tht they can increase the average revenue per user.

The question is how can facebook do it? Their algorithms can not change overnight that can make ppl click on them. another way to put it is with 800 million ppl on facebook and a large number of daily users why is that their revenue has not been able to catch up with google's, nd will it do anytime soon?