Why do the trachea need half rings while the bronchi have rings? We can see them in the animation☝🏻 Behind the trachea lies the esophagus and it’s tightly attached to it. And since it has peristalsis (and therefore deforms) - the trachea faces it "flat" and "ringless" side. And also the trachea has a support on the tissues of the neck, which facilitates the task of the half-ring. But next to the bronchi are the lung tissue and vessels - there is nothing to lean on. So they rely entirely on their own fixation mechanism - the rings.