It is very expensive to raise a a child to adult good, and very, very expensive to train them to be a doctor. Or you could get a doctor for no expense from abroad.
And even if you wanted to educate more doctors within the UK you would need the facilities and resources to do that, which simply don't existnand are hard to setup.
And if you do go down that route then you need the student applicants. There is no evidence that even with more capacity more people would start a medical degree, even if they were good enough, not with the NHS salaries and work conditions.
Which brings me to the next point. Even if You invested significantly to handle more medical placements, you need to prevent the graduates going abroad or working for big pharama etc.
