Well, I think you've pointed out and answered part of your question. Public universities generally have little/much smaller endowments by comparison because th

Well, I think you've pointed out and answered part of your question. Public universities generally have little/much smaller endowments by comparison because they rely on government for their steady stream of revenue. And because of that they can, and have pressure to, fulfill policy-based goals of educating students at little to no cost, or heavily subsidizing it. Some public universities are acting according to the incentives they've been given, and accumulating their own endowments to insulate against political unreliability, and you can also see why college sports are such an important revenue stream for them as a result.