Branding.

Remember the iconic dancing shadow iPod commercials? The person was not the focus; not even the iPod was the focus. The white headphones, unique at the time, were the focus.

Aftermarket black is available for $100 or DIY with electrical tape on stem.

https://m.imore.com/these-are-best-ways-personalize-your-air...

Agree, in black they would look a lot less like q-tips.

Because Apple's main draw is their branding. They want everyone to know that you have an apple product. Ever noticed that iphone cases have a little cutout in the back so that apple logo is still visible?