The problem is that, often, the amount that children do for the parents slowly creeps up as the parent(s) becomes less capable.
With my dad he had swollen legs in 2016 which he didn't tell me about until I saw how unwell he was. I got involved in helping him navigate the GP and cardiology resulting in multiple medication changes and an operation to fit a different pacemaker.
I thought I was only helping him get back on his feet but then realised mum's dementia was pretty bad and dad needed support for her. Mainly moral support at first but then more stuff landed in my lap to free him to just take care of her.
Soon I was navigating mum's dementia diagnosis to get medication , attendance allowance application, all medication requests and medical appointments, Covid online grocery shopping (which continued for 3 years), blister packs, parents not being able to understand the blister packs, pushing them to accept a carer twice a day to dole out the meds, attending about 10-15 hospital appointments a year with them, stopping dad driving, a second dementia diagnosis, a second attendance allowance application, more frequent carers, legs swelling again with no viable treatment options this time, Intensive Care at Home service, district nurses, care home selection for mum in prep for dad passing away etc etc
And all that is on top of visiting and staying with them in a dirty house I had to clean on arrival, sorting out any house or car problems, trying to spend quality time with them while working full time from their house. Neither were suddenly incapacitated so the amount I was doing just crept up over 7 years until I was reaching breaking point. And while they were incredible grateful, they became so focussed on their own needs and health issues that they couldn't see the burden it placed on me.