DELTA2ALPHA, In answer to your quesion-(Why MACV and the MC came to the conclusion that KSCB should be abandoned is beyond me.......)

Khe Sahn, Con Tien, Rockpile, Vandy were all part of a support network for that dam*ed McNamara Line disaster. Those bases & a few more were designated 'c' bases, and supported a string of bases designated A-1, A-2, A-3, etc, that was supposed to stretch from the S China Sea for about 50 Km I believe. Strong Points I think they called them. It was started in 66 or 67, to interdict NVA from the north. When Tet occurred, it took DoD by surprise, (but no one else)and they realized the McNamara Line was ridiculous. Khe Sahn was no longer needed to anchor that part of a line that didn't work anyway, so it was abandoned until the Laos incusion in 1971.