That can happen even when folks have children. My husband worked with and developed a friendship with a gentleman twenty years ago. He had two children. After his wife died, the man lived alone and soon could no longer care for himself. My husband cooked every meal he ate, cleaned his house, bought his groceries, literally, did everything for the man.
Eventually, hubby realized he needed full time care, so we placed him in an assisted living facility. His retirement monies paid for half of the expenses, we picked up the remainder. The last few months of his life were spent in a full care nursing home. He no longer recognized my husband and in a short time, died in the nursing home. We never saw his children once prior to his death - and they live in the same town. They did, however, manage to go by the nursing home immediately after the funeral and take the tv, wheelchair, and possessions we had purchased for their father.
I can totally relate to what you say. I befriended a woman in a similar state -- bought groceries, took her to church, etc. When she complained about her back hurting I bought her a new mattress. She died while I was on vacation/picking up my daughter from college.
This woman's daughter, who lived just a couple miles from her and had refused to even visit her when she was alive, did the one thing her mother feared she would do when she died. The daughter cremated her, because it was cheaper. I don't know what I would've done to help had I been in town. But, I have never known a colder woman in my life. I was told that when she was told that her mother had died, the daughter exclaimed, "Praise the Lord!"