I love USB-C for charging and data and display. But it does not replace 3.5mm. Aside from the things mentioned so far in the comments here, a fundamental problem is that now headphones need DACs in them.
The engineering specification states that an analog headset shall not use a USB-C plug instead of a 3.5 mm plug. In other words, headsets with a USB-C plug should always support digital audio (and optionally the accessory mode)
I love USB-C for charging and data and display. But it does not replace 3.5mm. Aside from the things mentioned so far in the comments here, a fundamental problem is that now headphones need DACs in them.
https://en.wikipedia.org/wiki/USB-C#Audio_Adapter_Accessory_Mode
That increases the cost of headphones and introduces a point of failure and makes things more complicated for the end user. It’s just not worth it.