The issue with simply putting the thrust levers full forward to command a go-around on any Boeing is that - unlike Airbus - the thrust lever position always determines the thrust command to the engine. So putting the thrust levers to the firewall will give you max TO thrust for those conditions - not always wanted, needed, or even desirable for a go-around (especially with a light aircraft).
It used to be taught for the PF to keep on hand lightly on the throttles during critical flight phases - especially final approach/landing - to know what the engines were doing, and to guard against a potential autothrottle malfunction. Don't they teach that anymore?