One consideration is that as time progresses, dividends will become less and less efficient due to NSR abandonment. Any NSR that is abandoned or forgotten about will still automatically receive PPC dividends. This represents lost shareholder value. The key difference is that buybacks deliver 100% of the value to all active shareholders, but dividends deliver 100% of the value to all shares, regardless of activity.
Because there is no difference between buybacks and dividends in terms of value delivered to shareholders, we should prefer buybacks more and more as time progresses.