Aesthetics. Short stem looks sleeker.
Form vs. function
Or, you know, design trade-offs like every other hardware ever made.
I don't want to feel like I'm wearing one of those customer support head mics. I'm ok with shorter stem, and never had a problem.
Honestly the stems always looked kinda dorky to me
Do they? I don't think so. Makes them look stubby and more like a hearing assistive device (not particularly fashionable).
They looked sleeker and more balanced with the longer stem and in the ear more like jewelry.