Because he knew he would be ridiculed for his hypocrisy. North Vietnam intentionally violated the Paris Peace Accords. The North Vietnamese negotiated in bad faith. The USA respected those Peace Accords. The USA was withdrawing military material and personnel as per the agreement, but the NVA were sending personnel and material into south Vietnam, and Cambodia.
It’s another of these false fabricated “rights” ( the “right to life”) which don’t exist in nature nor in non- western societies where there are No Rights whatsoever.
Any “ rights” which do exist are hard fought for in blood and enshrined in the enforced laws of free nations, which for brevity are encapsulated in the idealistic, high- minded, beautiful even, UN Charter of Human Rights, which rights actually existed in the west from England’s “Glorious Revolution” Constitution 1689.
These rights are basically the right for government to defend - maintain- educate you in exchange for tax and not unduly interfere in your life. Not Intended to “ keep you alive at all costs in defiance of nature” which is where we are in UK and Canada with the stupid Covid lockdown tyranny and where NHS grossly abused by people who damage themselves by ingested toxins or foolish injury ( accidents aside)then demand NHS ( other peoples money) to fix them with new organs, joints, drugs etc.
Lately these rights were predictably extended by the Marxists to include other false rights like “right to work” , “ right to travel” , “ right to attend university”, “ right to emigrate anywhere”, etc.