The National Audit Office said in June:
"DfE is accountable for providing those bodies responsible for school buildings with the funding and support to enable them to meet their responsibility to ensure school buildings are safe and well maintained.
Following years of underinvestment, the estate’s overall condition is declining and around 700,000 pupils are learning in a school that the responsible body or DfE believes needs major rebuilding or refurbishment.
Most seriously, DfE recognises significant safety concerns across the estate, and has escalated these concerns to the government risk register.
Although it has made progress in the last year, DfE currently lacks comprehensive information on the extent and severity of these safety issues, which would allow it to develop a longer-term plan to address them. It has announced that, where RAAC is identified in schools, it will provide funding to mitigate any immediate risk.
DfE has improved its understanding of the general condition of school buildings. This has helped it to allocate funding based on better estimates, and target schools assessed to be in the poorest condition.
However, there is a significant gap between the funding available and that which DfE assesses it needs to achieve its aim for school buildings to be safe and in a good condition for those who learn and work there. Funding is also often used for urgent repairs rather than planned maintenance which, as DfE itself acknowledges, risks not offering good long-term value for money.
DfE must ensure that its approach delivers the best value from the resources it currently has available."
Basically, the heads, the responsible bodies and the DfE (the civil servants) know that the buildings are in poor condition and/or dangerous, but the government doesn't give a shit about kids' safety or their education and doesn't want to pay for it to be improved.
No point in wondering why heads haven't done anything about it, we know exactly why.
No point in wondering why the DfE haven't done enough about it, we know that too.
Money has been urgently asked for by everyone involved and those critical requests have been rejected by those in charge of the purse strings, including by our now Prime Minister when he was Chancellor.