Facebook is a big company and one of the most famous social media website. Even my neighbor's dog has an account on Facebook. So, it won't be surprising that many will but and support it. This is also a good opportunity to introduce cryptocurrency to the public since many still do not know what is it aside from bitcoin. There are still people that I know I'm real life that only knows about bitcoin. With this great example, people might see crypto in other light.
It is right that there are a lot of people who are using facebook but there are some points which are that firstly the owner of facebook is facing some issues from his government in starting his coin and other point is that many people who will not need any payment system in facebook will not use its coin and will just use facebook for connecting to other people.