I think that it depends on the relationship. It shouldn't be a given.
I cut my narc Mum out of my life in my late teens. I feel absolutely no obligation to get whatsoever. Whenever there was contact, it was always challenging and she was always trouble.
My Dad on the other hand would do anything for us. Still pick us up from the pub at age 30 if we asked him to. Did my washing for me when I was at uni. Would come running if there was a problem with my car or at my flat. There is nothing I wouldn't do for him. Now that he has dementia, I am fiercely protective of him and do what I can to keep an eye and look after him. He used to say to us 'If I go doollally, drive me miles away and dump me on the side of the road'. There is no way we would ever do that but it shows his selfless nature.
My Stepmum can be lovely but has always puts herself first. When I wanted to meet up with my two babies because I was feeling lonely she'd usually be too busy even though she was retired.
So, I do what I can for her in the sense that I'm good at paperwork so made sure she has everything she is entitled to plus will give her lifts to appointments if I'm free. However, I feel no obligation and only do what suits me.
Sometimes I avoid her because she tends to scapegoat one of us amongst our siblings for months at a time and is very paranoid. It's part of her dementia but she was always a little bit odd like that so part of her personality. She could never understand why my Dad went out of his way to help us. So, I will help to a certain extent but not always drop everything, if you see what I mean.
So, what goes around, comes around imo.