What is the benefit (to the company) of paying to train a junior, which costs their wage, along with a significant proportion of a senior’s wage, if there is no long-term savings on the junior’s wages later on? This seems like a prisoner’s dilemma where every company counts on another to do the ‘apprenticeship’ training.

In other sectors, juniors are paid a subsistence wage for a few years, so they are still profitable for the company during training. A plumber still needs a cheap pair of arms to move around a bathtub.