Web server control panels like cPanel and Plesk make the job of managing different accounts and sites easier by adding a UI layer on top of common server applications.
They're typically used by web hosting companies that sell web hosting services to aid with the above, and to make it easier for their customers to manage their own accounts and sites too.
Control panels take up resources, cost license fees, and add a layer of bugs too however. Since large non-web hosting oriented companies are not concerned with the same functions as a web hosting company, they typically have admins who are highly familiar with server applications and don't find a need for control panels.
With that said, even with 20+ years of system administration, I often use them with large businesses, especially if less technical people need to perform some admin functions, like creating email or FTP accounts. They also offer a lot of built-in applications and automatic updates for the core applications they run on top of.
So in short, I don't think Facebook or Google uses cPanel, and if they do, it would be departmental and not site-wide.