In my experience there are two reasons: 1) the crumbling NHS means that children’s health issues are not being addressed 2) Academy chains - some academy chains are very rigid, almost corporate-like environments. This lack of adaptability takes away autonomy from teachers and makes it difficult to make adaptations for students. Teachers are leaving in droves: school avoidance is going through the roof.
edit: actually there are a few other issues too- like the very dry curriculum with less time for creative subjects, the lack of break time/outside play.
I think there is a loss of resilience among families since Covid too. Low employment, low wages, COL crises etc have made it stressful for parents, leading to financial difficulties, health and mental health difficulties (again, not helped by our crumbling NHS). These problems have an affect on children. Suddenly, less family time because everyone is working, parents have less time to help with school work. Parents are more stressed when around their children and may no longer be able to rely on family for help and support because family are also stressed, broke, unhealthy and overworked. Less holidays and relaxation time, less money for enrichment and hobbies - the things that help kids regulate and learn so many skills like self-discipline, self-esteem, resilience.
Many parents are millennials - the generation that were told that if we went to school, worked hard and got good marks we would do well. A lot of us did those things and got stuck in minimum wage jobs anyway. We know that education and working hard doesn’t pay off, so we are less likely to push our children into school (especially when all we hear about schools is how awful behaviour is, how horrible the general environment is, how stringent the rules are - silly uniform rules, rules about eye contact and going to the toilet etc).