It's also not necessarily indicative of anything. $100M is nothing for Zuckerberg, about 0.05% of his estimated net worth.
For context, excluding billionaires, your average 42 year old American (Zuckerberg's age) is worth about $135k*. 0.05% of $135k is about $68.
Given the choice, would you spend $68 to completely cover you just in case the world falls apart? Most people would. I certainly would.
*That still includes some pretty wealthy people that skew it higher, so don't feel bad if you're not even close in net worth. I'm sure not!