This is an issue in most countries, not only UK.
The job market is not prepared to fulfill the promises the talent expects, and in places like SV, what you get is the STEAM version of Hollywood, where every waiter dreams of being the next movie star, and there can only be so much.
Except that not so long ago the dream mostly came true. For many decades an engineering degree was a golden ticket to middle class financial stability and job security. Both in Europe and the US.
Nowadays that is no longer the case. Mostly because of international competition. People are still completely in denial, that there are people in China who do just as good of a job as they do, but for half the wage. Even more striking in software, where outsourcing to India is very common.