You've seen the Type C - 3.5mm headphone dongles right? They're so tiny and cheap.. did you think they could be active? :)

There is also a debug mode that manufacturers can use to send arbitrary debug data connections on the usb-C connections. (manufacturers used to do this over microUSB as well)

USB-C tries to be one universal standard that covers everyone's use cases (https://xkcd.com/927/). Some phones used non-standard modes in their USB connectors which output analog audio in the USB pins, to be used with a passive adapter to a 3.5mm socket. So USB-C added, in an optional appendix, a standard mode for that use case. It's completely optional, so you only have to implement it if your device wants to output analog audio in the USB connector, or if your device is one of these passive adapters from USB-C to a 3.5mm socket.