The 3.5 mm jack has several advantages over micro-USB:
* Omni-directional insertion. (Yes, along an axis, you pedant.)
* Graceful degradation among various formats - mono, stereo, with and without mic.
* Sturdy.
* Can be made (reasonably) water-tight.
... and let's not forget ...
* Ubiquitous as fuck.
Micro-USB was only announce in January 2007, and became the most widely used by December 2010, though Apple users have been on Lightning since 2012. So there was maybe a 2 year window for micro-USB dominance. That's not ubiquitous.
* Omni-directional insertion. (Yes, along an axis, you pedant.)
* Graceful degradation among various formats - mono, stereo, with and without mic.
* Sturdy.
* Can be made (reasonably) water-tight.
... and let's not forget ...
* Ubiquitous as fuck.
Micro-USB was only announce in January 2007, and became the most widely used by December 2010, though Apple users have been on Lightning since 2012. So there was maybe a 2 year window for micro-USB dominance. That's not ubiquitous.