This is a really complex topic with so many aspects affecting it.
SEN Provision
There isn't the proper funding in education. There need to be more schools for special education and more with enhanced provision and well-funded, well-supported units. Some of the children currently being forced into mainstream settings cannot cope there, which has an impact on them, their families, the staff and the rest of the class. Even for those who can cope in mainstream, it's becoming so difficult to get help for them and almost impossible to hire support staff to aid in this.
Parents' ACEs
There are a lot of parents with their own adverse childhood experiences and these absolutely colour how they see their child's experience of school. Parents who struggled with school (academically, emotionally or socially) are more likely to keep their child at home if they think their child is experiencing something negative.
Pressures on the NHS
For a few children, the NHS backlog and the difficulty of getting appointments and treatments mean that they end up unwell for longer or get a lot worse in the meantime and have to take more time off school.
Pressures on schools
Some of the current expectations on schools are just ridiculous and needlessly high stakes. This creates a more highly-pressured system which absolutely can be felt by the children themselves, increasing their unwillingness to be there.
Retention and Recruitment Crisis
Whilst there are exceptions, there are a number of graduates who would make excellent teachers but they don't choose to go into it because the career just isn't attractive enough to them. You can add to that the lower levels of applicants and the constantly dropping standards for entry (and passing) teacher training. Then consider the level of experienced and competent people leaving the profession. Some children will genuinely be having a shit experience because they don't have the right (or any) teacher.
Ineffective parenting
There are some aspects that are the fault of the parents. Unfortunately, we don't do enough as a society to develop and refine the parenting skill, seeing commenting on parenting as a personal insult rather than having a culture of improvement. As such, there are just some ineffective parents out there who have been doing a shit job for years. That leads to poor attendance.
Importance of Education (parents' perspectives)
Whilst the majority do value education, there are some parents who just don't. They don't care if their kids do well, they don't care if they get qualifications and, to be honest, they don't care if they attend. There are some areas of really low aspiration where I have genuinely heard parents say things like: "Well I did shit at school and I'm fine so he doesn't need it."