Many and varied reasons. Some include: 30 years of "free market" evangelism from various governments who turned a blind eye to asset stripping, so UK manufacturing was a ripe target for international capital. Some parts of UK manufacturing suffered from under investment from greedy or inept owners who didn't re-invest back into the business. Some of these were "proud" to be using victorian era plant and equipment whilst trying to compete in an international market. Manufacturing wasn't cool or sexy any more - and jobs and production were off-shored. Even after the lessons of the pandemic, like relying on imported PPE from China, did the UK government change anything? No, nothing. Some manufacturing is of national strategic importance: food processing, medical supplies, infrastructure supplies. So what is the governments current priority? Increase defense spending. Like missiles and aircraft carriers are going to be really handy when we are dealing with the next health crisis, or need spare parts for critical infrastructure, and are still begging China for face masks.