I think kesstrel has hit the nail on the head. It was well documented that the parents whose children needed SureStart were the ones least likely to access it.
It is often a problem to do with low attainment of the parents, but not necessarily. We all can see parents who are not very interested in reading to their children, or singing, or playing games and generally developing their children. Poorly educated parents may struggle to understand child psychology, but they could receive guidance on what is the best way to engage with babies and toddlers on a practical front. Health Visitors and baby clinics used to help with this. We now need new interventions to help these children and they need to be identified earlier.
Having said that, a Nursery Nurse I know worked in a family centre for challenged families and time and time again the same advice was given to the parents but it was rarely followed resulting in the same issues occurring time and time again. Some people lead chaotic lives and just do not engage with what they are told. Most people posting on here will have no experience of that. These parents have little expectation of their children, they just need a roof over thier head, a stable relationship with a partner and food on the table. I have also been aware that parents are grateful if their children can read and write because "that's more than I can do". Often the parents were very switched off from education and do not necessarily see the benefit of a good start. Some do.
Where parenting is a struggle, children are not spoken to, are plonked in front of a screen or TV, not interacted with because parents are on the phone all the time, and the children are generally seen as an inconvenience. Sometimes the parents have a very poor vocabularly themselves. Where I live, there are very pleasant new housing estates with mostly privately owned houses but plenty of those children have poor skills when they start at the nursery attached to the schools.
There can also be issues when both parents have to work and then want time for themselves, (understandably) and not the children, at weekends. How many times do we see young children dragged around shops on a Sunday instead of having a great time in the park? Or spending long, long Sunday lunches in the pub as the parents become steadily more unsteady and let the children annoy everyone else. Plenty of people do not intend to spend time with their children beyond basically caring for them and buying things for them. A lot of the children are not neglected as most of us would understsnd it, but they are neglected in terms of early stimulation and interaction with adults.
Sorry for the ramble. Iam getting myself a coffee now!