To summarize Cook’s major defense here, he’s basically saying that headphone wires have always been the devil. They weigh down your earbuds, causing them to wiggle from your ears, disrupting the pleasure of listening to Spotify or hearing your best friend’s gossip.
Or, as Cook said himself: "I've been wearing them [AirPods] for a while. And because they don't have wires on them… The wires tend to help the earbud to fall out, because it applies weight on those. By snipping the wires, I have never personally had one [AirPod] fall out."