This may seem like a naive question, but its one I've had on my mind while working through readying my applications for a PhD in the UK. It seems bizarre to me that PhDs here are not funded by default - from my point of view, a PhD is effectively a job. It is a sort of long term graduate program for working in academia. From this point of view, it seems absurd that one could end up being in a situation where they might actually have to pay to pursue one.
One possible answer is that universities are simply admitting more students than they are capable of funding. If that is the case, then why is it the case? Surely having fewer, better funded doctoral candidates would not only improve the lot of many "students" (employees, in my view), but it would also have beneficial impacts on the employment prospects in academia for PhD students after they finish, since there will be fewer people competing for the same number of openings.
What are the incentives and cultural motivations here that keep the system as it is? How different is it in other countries? (I have heard, but been unable to decisively verify, that many European unis treat PhDs as the jobs they are).