Here’s the long answer:
We do not include a USB C DisplayPort capable cable because the maximum length is limited to “Cable length should be 2.0 m or less for Gen 1 and 1.0 m or less for Gen 2.” This would only leave about 0.6m (2ft) of cable sticking out of the back of the XOOT_Pro arm. That is not enough slack for most customers.
We include a 3m (9ft) USB C to USB A cable (usb spec 3.0), this is the same length as the included video cables. This ensures that all cables should be long enough to reach most customer PCs.