When you click the block option the following message pops up.
The actual reason for this is not that Mark is the Founder cum Owner of the Social Networking Giant so that he shouldn’t be blocked, According to an article of Mashable, It is a way to prevent trolling from a large number of users against certain people.It is termed as the Product of a safeguard built into the site.
It means that, if a single account is blocked by a large number of people in a short interval of time then the safeguard will kick in and will also prevent any furthur blocks from the users to the same account , just in case to prevent the user from Trollesters and the corresponding viral campaign. Simply Facebook’s acts as the automatic block blocker to prevent from more blocks.
After all Mark Zuckerberg who is one of the popular accounts on Facebook with over 40 Million followers. A lot people are trying constantly to block him on Facebook. The same safeguard is applied to Mark Zuckerberg’s account making it unable to block anymore.