This is what I was saying to my husband -- you can't expect someone on £30K to apprentice for minimum wage for a more specialised £50K job being done by a non-EU immigrant. Nor would it make sense to have an entry-level person apprenticing for that specialised, high-level position. Tier 2 holders don't (generally) get through the system because they're doing entry-level or early-career jobs, or skilled manual labour; they're doing jobs that have extant education pathways and career trajectories.
Exactly - most Tier 2 visas are for jobs that are so specialised that there are only a small number of people in the world actually capable of doing them... because those people either have a certain mindset (i.e. a genius scientist or a world-renowned surgeon or medical researcher) and/or several decades of experience and knowledge and recognition behind them which means they are able to do that specific type of job.
Those aren't the kinds of jobs that you can just train up an apprentice for. They usually require high-level academic qualifications, plus several years of experience in the field.
At 25, I was as trained up as I could be at that age for the field I wanted to work in (geophysics), which just happened to be one of the fields that is listed on the Tier 2 Skills Shortage list. I had 2 degrees, 6 years of studying and 2 research dissertations behind me; I also had 10 years of customer service experience and knowledge/experience of several different scientific computing programmes and languages.
But could I get a job, even in a 'shortage' area? No, I couldn't. Because the companies weren't hiring recently-trained graduates, they were hiring project-management level employees who had at least a PhD and 10 years of experience. There are not many geophysicists in the UK who are trained to that level, and the field is by default an international one - you have to go where the jobs are and where the research centres and geophysical companies are based, and most of them are overseas.
So, the companies I wanted to work for were no doubt having to hire experienced workers from outside the EU, while I couldn't get a job with them and ended up working in retail in the UK at just above minimum wage.
It's very common in that field to move abroad to work, especially as the job opportunities are more lucrative and plentiful in other countries. Several UK geophysics/geology graduates that I know are now working abroad - in the US, Norway, Tokyo, Australia etc. (I moved to the US myself to further my qualifications in the field)... so even if we do train up people here there's no guarantee they will stay in the UK to work... especially not when they can earn double the salary to do the same job in countries like the US or Australia.