1. Facebook's job as a corporation is to make money
2. Making money for FB is largely based on MAU
3. Playing politics and censoring the chosen world leaders of large portions of their user base is a probable way to lose those users, and thus, money
The assumption that people leave assumes that there is a different place to go to, which for most people, there isn't because social networks are exactly that: networks. Unless you have a small isolated network that can move all at the same time, it is not likely that people will single themselves out.
Censor itself of course can mean any kind of redaction, not just limiting freedom of public expression. Facebook has rules which they use to filter (and thus, censor) content on their platform. I'm not sure it has an exemption for a government person in there.