Question

Why do arteries need thick, strong, elastic walls ?

Answer 1

To sustain and withstand the high pressure of the blood being pumped by the heart to all the parts of the body.
Explanation ;
Arteries are the first vessels that carry blood from the heart and transport it to all the parts of the body. Since they must receive the blood directly from the heart which pumps the blood at a pressure sufficient to enable circulation, they need thick and elastic walls to both sustain the pressure (and so keep the blood flowing) and to withstand the pressure (and not get affected by the pressure)
The elasticity is what sustains the blood flow by enabling the arteries to expand and contract rhythmically with the systolic and diastolic pressure of the heart.
The thickness prevents tearing of the artery walls by the pressure of the blood.