There is an old saying in conflict theory that if one side is saying "What is mine, is mine and what is yours is negotiable" and the other side plays by those rules they are going to lose.
Almost all the fighting was South of the DMZ we never once sent a major battle force North of the DMZ to take and hold ground. Yet the NVA and VC were constantly attacking South of the DMZ. Hell we never sent troops into Cambodia to disrupt the Ho Chi Minh trail until Nixon and he only did so in attempt to get a stronger position in the peace negotiations. Nixon finally mined the harbors in the North to stop the influx of war materials into the country by USSR and China but again that was well towards the end and to get a stronger position in the negotiations.
You don't win a war by just killing people you also remove their ability to make war by taking all their territory and destroying/denying their resupply chains. But apparently we don't do that anymore.
You can’t win a football game if you never cross the 50 yard line.