Systolic and diastolic blood pressures are affected differently by exercise? what could account for the difference?

Your heart has to work hard to pump more blood during exercise for each contraction, accounting for the increase in the systolic blood pressure. Diastolic pressure tends to not change at all or change slightly. The reason for this is that since the blood flow is increased during exercise, our arteries dilate, making the diastolic pressure stay the same, or decrease slightly.

That would be a working theory.