Those 2 chips play a different role.
The STN1170 is a CAN protocol decoder that takes logic level voltages and decodes CAN messages.
The TJA1048 is a CAN transceiver to convert voltages on the wire to logic level voltages.
In the Carloop, the microcontroller is the CAN protocol decoder. There's no need for the STN1170.
If you wanted to support SW and MS CAN, you would need to make a new board with additional transceivers to convert to the voltage levels expected by these pins.
Let me know if that makes sense.