You seem to be one of the many (often but not always girls) children who felt less loved than other siblings and now, in their parent's old age, bend over backwards to show Mom that we really are lovable after all. See, Mom? Look at all I am doing for you? And where are the other two? Where is the all time favorite older girl?
I am speaking from bitter experience. I lived with Mom for 5 years and the worse her dementia got the more I tried to show her I was the one and only child who would give up everything to help her. I neglected my teeth because I had no time to go to a dentist, re****ing in thousands of dollars of dental bills after I was finally settled where I am now.

I slept hardly at all, my whole life revolved around Mom and my job. I had no life for myself.
The result of these 5 years of devotion: Mom does not remember that I ever lived with her.

And while I was there she resented me and blamed me for her confusion. The best loved eldest sister also blamed me. Now, when that sister calls her, it is Christmas and her birthday all in one.
I was the unwanted second daughter. I spent many years of my life trying to make Mom love me at least as much as the others.
Mom is still my role model and I do not blame her for resenting a second baby 13 months after the first in the final years of the Great Depression, with no money. I understand. But it took me a long time to figure out why I clung to Mom so much, and refused for way longer than necessary to have her placed in a good NH. My sister never did anything for her, and remains the favorite. Go figure.
There must be a deep psychological reason for it. If you figure it out, let me know!
Love,
Martha