I believe he was saying that short-termism (which his belief is everywhere and I assume he has this opinion based on external beliefs not listed here...) is the root cause of this. Not many people hire junior devs anymore.

I tend to agree with him, and believe it has a lot to do with the death of "lifers" in business.

The quickest way to progress a career nowadays is to jump every few years, and that applies to both management and tech people. If people do this, what incentive is there to properly mentor a junior developer? Train them up for them to get nabbed in a few years?

There is not much loyalty in both directions nowadays and that has some genuine downsides.