Some of it IS down to piss-poor parenting. I speak from experience.
To be clear, my mum and step-dad weren't on benefits, so that stereotype isn't a factor. My mum was a 'SAHP' (and that's written like that for a reason, not because I have any issue with SAHP's, but because my mum seemed to miss a key component of the role) but my step-dad earned really quite good money.
However, both smoked, both drank, both ate ridiculously large quantities of takeout instead of cooking and my mum, at least, was, frankly, lazy, with a chip on her shoulder the size of the Isle of Man. And, yes, I realise it isn't nice to talk about your mother that way, but it's simply the truth.
I was isolated from a lot of it, because I also had the care and attention of my Grandma, my Dad and my Great-Aunty.
My brother and sister, however, were considerably younger than me, and by the time they were at school, my Grandma had died, my G.Aunty was too elderly and ill to help and, obviously, not being their father, my Dad was not in the picture for them. If it gives any indication, my DH told me recently that there were a few years whilst I was at Uni were his mum - HIS mum - had genuinely thought she would end up caring for my brother and sister when they inevitably ended up with me.
I can quite clearly recall the moment that I realised just how much of the poverty my brother and sister endured was caused directly by my mum and step-dad's attitude. I'd left for university by then, and had come home for a visit, bringing with me my then new boyfriend DH. My mum asked him how much he was earning. He was in his first job, at 19. His answer was £9,500 a year.
She laughed, looked at me and said, 'That's all? That wouldn't keep me and your step-dad in fags and beer.'
That comment came the day after I'd bought my 9 year old brother a new coat and some new trainers because his existing coat was too small, the trainers had holes and it was January. My mum had, apparently, told him she had no money.