Some fluid dynamics in addition to some of the other answers: Locally, the law of Laplace states that parietal tension is proportional to the pressure and to the radius, meaning as the radius decreases, the parietal tension also decreases.

Also, as per Bernoullis principle, this decrease in radius doesn't increase blood pressure. Velocity is increased, but pressure decreases, as the total energy of the blood in the vessel leading up to the narrowing has to be equal to its energy as it passes through the narrowing.

This also explains the increased risk of aneurysms rupturing. Their increased diameter leads to higher, not lower, pressure.

Moreover, this works locally, regardless of parallel blood vessels: a dilated ventricle leads to increased parietal tension not by increased blood flow from parallel blood vessels - there are none - but from the same quantity of blood passing through.

Edit: typo