Why do semilunar valves not need tendinae but atrioventricular valves do?

Question

Inside the heart the atrioventricular valves (AV) have chordae tendineae to prevent the backflow of blood into the atrium when the ventricle contracts.
Since the AV and semilunar valves are effectively the same thing but in different locations, it would make sense that the semilunar valves also need chords to prevent blood backflow. But they do not. Why doesn't blood flow back into the ventricle after the semilunar valve closes?

practiZ · Answer

Unlike atrioventricular valves, semilunar valves' leaflets are concave, somewhat like shallow bags, which, during the diastole are filled with blood and therefore are pushed back to touch one another and so close the valve opening.
Here's
a good gif to visualise.
Some reference: 4 Valves of the Heart: What Are They & How They Work

Why do semilunar valves not need tendinae but atrioventricular valves do?

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