Why are these capacitors needed on the USB-C CC lines?
The Power Delivery protocol uses slow, 300 kbps signaling rate, with edges limited to 300 ns. And the driver uses 50 Ohm impedance. With 400 pF load the time constant of this network is just 20 ns, so the cap doesn't have any effect on PD digital communication. Yet the CC pins are multi-functional, so smoothing the signal a bit doesn't hurt. In fact, the BMC PD receiver does require the 200-600 pF cap per PD specifications, see Table 5-19. Note that the old (faster) BFSK signaling mode is depreciated in PD 3.0 Specifications.