IMHO it comes down to the Housing Theory of Everything [1].

The UK doesn't produce anything anymore. The best returns on investment aren't in productive output. They're in hoarding land. This is exacerbated by an anachronistic system whereby artistocrats are still significant landowners (eg the Duke of Westminster). The UK badly needs land reform but the system is designed to protect landowners through the House of Lords. Up until only fairly recently, the House of Lords still had hereditary peers.

This relaly started in Thatcher's time but was made significantly worse in the aftermath of 2008. The UK government chose to bail out the banks at the expensive of taxpayers and then pay for it by crippling the economy with 15+ years of austerity measures.

So there's been a revolving door of British PMs because literally none of them have been interested in addressing these core issues. What we really need is another Oliver Cromwell.

[1]: https://papers.ssrn.com/sol3/papers.cfm?abstract_id=6571818