AC coupling caps on USB interface
The question has to be why these caps aren't there in the D+/D- lines.

The D+ and D- lines of USB (any, also USB3) cannot be capacitively coupled, because an USB1 host detects the low/full speed of the connected device by checking whether D+ or D- is connected to 5V through a 1.5kΩ resistor. The caps (if any) are inside the device, behind that 1.5kΩ resistor.

Keyboards, mice and game controllers often are low-speed devices to allow cheaper cables and controllers, so these are still common.

USB2.0 uses the same D+/D- pair for communication, so it keeps the DC coupling into the device.

This requirement isn't there for the additional RX and TX pairs of USB3.0.