Is it worth investing in training when the employee might leave in a year for greener pastures as developers commonly do? It's a two way street.
I've personally seen two bootstrapped companies locally who invest in college graduates and pay them slightly below competitive wages; they have some of the most loyal employees, and more competition for job openings than they could ever hire.
It's not ideal for every company, for sure, but it does work.
On the other hand, in most or all of the companies I've been somehow related with, more experienced developers have naturally invested their time in helping juniors learn.
Vs 6 months of training at fulltime pay, would be maybe $70k cost to a company?
Yes, it is far cheaper to interview tough vs train employees (for right or wrong)