
Finally over a month later, a person familiar with the product's development told the Wall Street Journal what the reason was. Apparently, Apple is having trouble charting a new path for the AirPods when one goes missing or the battery dies.
Typically in Bluetooth headphones, one side receiving the signal then transmits the data over to the other side. This is not the case with AirPods.
With AirPods, Apple added its in-house designed W1 chip to each earpiece. This means that both pieces are connected via Bluetooth separately, and when one goes missing, the other can still be fully used.
Currently, Apple.com lists the AirPods as "coming soon". Tim Cook also mentioned that the wireless earphones would be shipping "in the next few weeks".