Why don’t public colleges and universities salt away large sums of cash during good times to tide them over during bad times? Because the internal politics won’t allow large sums to sit undisturbed. Because the external politics are such that when times get bad, legislators see those reserves as excuses to cut funding. (Apparently now in Massachusetts, the state is even applying this to endowments at private universities!)
Why don't governments do so? Same reason.
BTW, the author of that post is a flaming liberal. You can tell by his second paragraph.