It was 1987 - Full Metal Jacket was just out, following Platoon last year. Clearly America loved grim, unflinching looks back at the US involvement in Vietnam.
It was 1987 - The A Team had just finished its run with its characters, "hunted by the government for a crime they did not commit", finally being cleared of robbing the Bank of Saigon. Clearly America loved corny 80's buddy-action shows about the hijinks of Vietnam vets, preferably with as much back-slapping and thumbs-up poses as possible.
Clearly, what America would really love is a show exactly halfway between the two - a grim, corny, unflinching buddy-action show about bro hijinks in Vietnam.
Tour of Duty, Opening Credits (Side note: small rural Ormond, sitting up in bed as the TV played in the next room, was _creeped out_ by the theme song of this show. Who were those nightmarish, primal minstrels?)