Universities, and I would guess charities as well, tend to liquidate their shares immediately to avoid conflicts of interest. Liquidating that many shares that fast would cause havoc in the markets.
https://www.gatesfoundation.org/
http://www.bezosfamilyfoundation.org/ <- Jeff's parents, not Jeff
> "we are impatient optimists working to reduce inequity"
Ironic considering that these foundations literally exist because of the consolidation of wealth and resources, aka, inequity.
And if the global trend of further wealth consolidation is any indicator, they're not succeeding.