Question

Why do arteries need to be thick muscular and elastic

Answer 1

Arteries (and their derivatives) form the pressure vessels of your vascular system.
This means they must be able to withstand pressure required to deliver blood from the heart to the rest of the body, particularly oxygenated blood from the left ventricle through the aorta towards systemic circulation.

Veins on the other hand largely form your capacitance vessels which convey blood volume.

Just be careful not to mix pulmonary arteries and veins though in terms of what they carry.