The mental gymnastics are due to the legal environment in the US and in particular on laws in many states that could send physicians who prescribe a drug for the purpose of ending a patient's life to jail.
But there are lots of drugs that have the possible side effect of death, and plenty of patients who decide that the risk-benefit of taking a drug is warranted even though it might kill them.
So therefore, everything has to be described in terms of "pain management" and "comfort" where the cessation of breathing is just a... potential side effect. If that, combined with the patient's standing orders not to intubate or perform any sort of resuscitative action in the event that they stop breathing, leads to death... well...
The euphemism that is frequently used is "palliative sedation" (or "terminal sedation", although that seems to be used mostly by people of the thou-must-maximally-suffer school of thought).