Much of the Vietnam War was an illustrated case of generals “fighting the last war”. In WW II and to a certain extent in Korea (and most earlier wars, in fact), the strategy is to “take ground”, especially high ground where artillery can be fired for greater effect. (High ground permits better observation of more territory, and when used as a base for artillery it effectively increases the range of the guns because of the ability to “fire down” on targets.) “Taking the high ground” prevents your enemy from taking it to use it against you, so it has always been a generally favored tactic in war, and the Americans at first thought they were fighting a “classic” war.
However, the Viet Cong did not operate as a “normal” army that the generals were used to fighting, or at least “had studied in war college”. They VC never had much artillery, and since their forces were far weaker than the Americans’, they had to adapt to guerrilla warfare tactics, hit and run, ambush, etc. where their smaller numbers and reduced firepower worked to their advantage, since it’s much easier to hit fast and then retreat a small force safely (over ground that you know better than the enemy) than it is to fight a set piece battle with forces you don’t even have.
Consequently, they didn’t much care about taking the high ground to use for themselves, but they knew that the American forces would want it, and they made it attractive, at times, for them to attack and attempt to hold such strategic strong points… and then they would mount surprise attacks against those points, not so much to take them as to weaken the American resolve to fight at all.
So it was a favored tactic to lure the American generals into such places where they could “take ground” and look good to their superiors because they were “advancing the war effort”, but then they could be ambushed through the VC tunnel system, through paths in the jungles, and by co-opting the villagers that the American and Vietnamese armies had to pass through to attack and reinforce positions.