Why doesn't atherosclerosis affect veins?

Atherosclerosis: There is a venosclerosis but it is uncommon. Atherosclerosis forms in part because of the pressure dynamics in the muscular walled arteries and arterioles. The pressure dynamic is much lower in veins.

Arteries/veins: Atherosclerosis is process that occurs in arteries not veins. The lay term for this is "hardening of the arteries" and is due to plaque building in arteries from high blood pressure, DM, high cholesterol, smoking and genetics. Arteries are high pressure systems and veins are low pressure. Veins are not affected by the plaque formation process.

Low pressure: We don't know everything about how atherosclerosis works, but we do know that there has to be a certain stretch on the wall for it to get going. Venous pressure is of course much lower than arterial pressure. In the pulmonary arteries, atherosclerosis occurs when, and only when, pulmonary arterial blood pressure approaches sytemic arterial pressure.

Atherosclerosis: Atherosclerosis develops in the portion of the artery wall that is muscular. There is no muscle in veins, so plaque does not develop in these types of vessels.

LowerPressure is Key: Veins operate at much lower pressures than arteries, typically <5 to max ~15 mmHg above atmospheric pressure (without gravity), do not stretch with each heart beat & have much less smooth muscle in walls than arteries. However arteries operate at pressures >100 to >200 mmHg above atmospheric pressure & stretch with each heart beat. Veins develop atherosclerosis rapidly when used as an artery.