No sources cited for any of the interesting claims, nor does this article actually answer the question in concrete terms. This is someone who turned their opinion on why his security is so expensive into a full length article.
Tldr the author thinks it's because so many people use Facebook, have strong opinions on their policies, and because Zuck as the founder is synonymous with the company.
https://medium.com/swlh/why-mark-zuckerbergs-personal-securi...