The flip side of this narrative is that Zuckerberg's massive undiversified exposure to Facebook equity keeps Facebook protected from activist investors seeking to potentially obstruct the mission of the company.  Some shareholders like that an investor like Ackman can't buy up enough of the company to install board members and start to start unilaterally shifting the company.  

Ultimately, it's a free country, if you don't like that Zuckerberg holds the reins at Facebook, don't buy Facebook.