Why to connect PIN 8 to PIN 10 on Arduino Mega to get SIM7000 shield working properly?

Hi, does anyone know, why the PIN 10 and PIN 8 should be connected when running SIM7000 shield on Arduino Mega? What is wrang with PIN 8 on Arduino Mega, that it cannot be used directly? What is the reason? It works fine, I just want to understand for situations, if I would like to adopt this for another board, e.g. ESPDUINO32. Thanks.