How can they though?
Example of my mum - ECT in 1988, brain damage. Diagnosis of EUPD. Was never fit to work from that point on. Had two children, married, husband walks out suddenly, now single mum to two children.
Still unfit to work. Benefits in that period were £80 per week. Dad didn't pay CSA.
Mum now has early onset dementia. She's not yet 60. In a care home. Can't speak, can't track with eyes, no voluntary movements - can't even lift her hand to scratch her nose - beyond reflex reactions - cannot walk. Can barely eat and drink. Doubly incontinent. Zero ability to care for herself.
At what stage could she possibly have saved any money to support herself?
Similarly younger sibling - autistic, mental health, LD. Very complex individual. Can do some voluntary work but would not be fit for regular full time employment at all. Barely gets enough to live off. Even if she did, she isn't allowed to save or her benefits stop.
In both cases - sibling will never marry. She will never have children. She will never fully independantly. She is permanently dependant on others for all her daily needs. She is mostly OK but she has her bad days.
Parent was never truly happy. Spent their entire life at the GP. Multiple suicide attempts. Only now that they are basically a shell of themselves, can I slightly comfort myself with the fact that her demons are I hope, long gone in her mind; albeit I have no bloody idea if they truly are and she just cannot communicate her distress anymore.
Both of them have been and for the rest of their lives will be dependant on state benefits. Unless someone takes my sister on to work full time, which is highly unlikely to happen sadly, she would need at least two adults with her supporting her through every shift. She does wash dishes at a cafe but that's as good as it gets, even then she needs a lot of extra help.
In both cases this situation is not their fault. My mum didn't ask for ECT. She didn't ask for brain damage. She certainly never asked for dementia, I remember telling her and the distress she had that night will haunt me for the rest of my days - I still wake up most nights sobbing from nightmares.
My sister was born as she is. She hasn't got the intellectual capacity to improve her situation.
I have always, always tried to look after them and have given up 30+ years of my life to do so but there comes a point where I have to care for myself, and let others take over. How can I possibly support two adults and myself on one wage? How do you do it? Believe me I tried, and I've had three nervous breakdowns before the age of 30 to prove it isn't doable.