Where are you getting this propaganda from? The US used carpet bombing in Vietnam and Afghanistan killing hundreds of thousands of women and children and still lost both wars
en.wikipedia.org
abcnews.go.com
As for preventing further PAVN/VC offensives, they failed.[
citation needed] In May 1969, PAVN/VC launched an offensive similar in size to that of the
May Offensive of the previous year.[
citation needed]
It certainly cost North Vietnam the effort and manpower to disperse and camouflage their Cambodian sanctuaries to prevent losses to further air attack.
It was stopped because of geopolitics as mentioned below:
When Congress, in the summer of 1973, legislated an end to U.S. military action in, over, or off the shores of Indochina, the only U.S. military activity then going on was air support of a friendly Cambodian government and army desperately defending their country against a North Vietnamese and Khmer Rouge onslaught ... What destabilized Cambodia was North Vietnam's occupation of chunks of Cambodian territory from 1965 onwards for use as military bases from which to launch attacks on U.S. and South Vietnamese.
It had nothing to do with losing armed combat with Vietcong.