Aside from the inappropriateness of judging others for their decisions on such a complex issue, there is something you are not taking into account. There are countless cases of couples in which the caregiver died before the Alzheimer's patient due at least in part to the very high demands and related stress of caregiving. Taking care of the loved one often takes such high priority that the caregiver neglects his or her own health. My father-in-law died in just this way. Now I am looking at the situation of my own parents, who are in their 80's, and the toll it is taking on my mother to care for my father as his Alzheimer's progresses. She has begun having pre-stroke symptoms, extreme stomach aches, and I can see she is exhausted. I am looking for an AL facility for them now.
Keep in mind that if the caregiver, with all the best intentions, exhausts him or herself and predeceases the loved one, the Alzheimer's patient will have a much harder time than if his/her spouse stayed healthy and remained available to them throughout their life.
"In sickness and in health" means different things in different circumstances, and sometimes the most loving decision is to get proper care for your sick spouse, care which may be simply beyond your own capacity. Please be more compassionate toward people who make this hard decision; you can be sure they agonize over it before reaching the conclusion it is the best thing.