It’s Apple so the answer is clear: shorter stems look nicer. Functionality be damned. You’re holding it wrong my dude. Nobody wants to look like they have q-tips in their ears.
Also each device has to be identifiably different by at least some small margin, so the people who care about measuring worth/value based on the latest devices and similar trash can reject people based on what they "wear", pushing up device sales.
The smaller the form factor, the closer they are to functional implants.