I think there is a lot going on.
Teachers are stressed and not enjoying thier jobs.
Resources are scarce so subjects have to find cheaper and cheaper ways of getting the same outcome. Which is fine educationally, but how boring is DT or art if you can't use lots of different materials in your projects, or science with fewer experiments.
Social time is cut as staffing lunch hours and afternoon breaks is impossible.
The gcses are too content heavy in some subjects so make it a race to get everything covered.
Years 7,8 and 9 get ignored as that key stage isn't the 'important' one. So they get the weaker teachers, or cover to make sure gcse classes get through.
The progress 8 /attainment 8 doesn't include enough vocational options and vocational offers tare cut as difficult /expendive to deliver.
Not all the problems come from school