Who replaces senior engineers if we stop hiring juniors?

I've been mentoring a graduate who applied to over 400 roles and got very little feedback, which pushed me to look more closely at what's happening at the entry level.

It seems like a combination of factors. Fewer junior roles, more experienced engineers in the market and teams getting more productive, which reduces the need for entry level hiring.

The part I find more interesting is the longer term effect. If fewer people can get into the industry now, the pipeline that produces senior engineers over time gets thinner.

Curious whether others are seeing similar patterns.