Goodness, OP, your opening post rings so many bells for me. My mother was never the maternal type, and some of the incidents from my childhood that are coming most closely to mind these days are the times when she didn't visit me when I was in hospital, or when I didn't get as many visits home as everyone else when I was at boarding school because she thought it absolutely obvious that she shouldn't be expected to travel for an hour to pick me up. There were kids there whose parents lived several hours away who saw them more often than I saw mine, and it hurt.
So now roles are reversed after she had a mildish stroke after my father's death, and has been gradually sliding into vascular dementia. I've spent years visiting her in her sheltered accommodation and more recently in hospital and in the care home she's just moved into. I wouldn't mind but for the fact that she is so determined not to help herself in any way and is desperate for any excuse to moan. In the early stages she basically refused to engage in any sort of rehabilitative treatment that might have helped her mobility, speech and ability to write, and whilst she claimed to be bored and frustrated she rejected every attempt to organise things she might enjoy, even when they required minimal effort from her. She had carers going in twice a day to help with various things, and more than once I or my brother heard her being incredibly rude to them.
Things actually improved while she was in hospital - although she wouldn't admit it, I think she quite enjoyed being able to watch what was going on around her, and when she said she was bored I could see it was perfectly justified. However, now she's moved into a care home where you would think her life was considerably improved, she's gone back to square one.
Matters came to some sort of a head this weekend when, having spent the morning working on clearing out her flat, I spent what turned out to be over an hour driving to the home (due to bad traffic) only to find her again moaning about utterly ridiculous things. It was "too quiet" apparently but she wouldn't put on her radio or watch the TV in her room because there was "nothing on". She claimed the staff weren't helping her with practising walking, but she wouldn't ask them to help. She didn't like what she'd had for lunch, but she chose it. I can just see a return to the scenario where she won't take part in anything the home has to offer by way of activities and will spend her life complaining how boring it all is. When I heard her muttering that she wished it was my brother who had come to visit, I was severely tempted just to say "Fine, you don't want me to visit, I won't bother" and walk out and not come back.
But I know I won't just because I would feel so guilty. And a part of me acknowledges that, when she had the stroke, nature probably intended her to die, and the end of her life would have been much, much better if she had. I'm really not sure that medical science is necessarily doing the elderly any favours, at least unless and until a cure for dementia is found.