>> What was the incentive for companies to train juniors into seniors in the past, post job-hopping era?

You get a lot in the interim!!! I started at Andersen Consulting (now Accenture.) The annual attrition was ~20%, but they still invested over a year of training into me.

But it worked:

- They needed grunt work in early years (me, working 75hr billable weeks). Not sure how much of this is viable now given LLMs

- They had great margins on the other four years. Not sure how much of this is viable now, as margins have shrunk in the past 25yrs as there is more way competition

- They used me to train the next cohort in years 4/5

- I appreciated the training and give them 60hr billable weeks on average for five years

It was a brutal and exhausing five years but i'm forever thankful to AndersenConsulting/Accenture for the experience.