The job market for top engineers is supply-constrained, as demonstrated by the rapid increase in SWE wages in the past 15 years. If you agree that top engineers are the primary input to these companies' success, then it makes sense for them to adopt a "hoarding" behavior.
In other words, these companies have over-hired as a way to prevent competitors from hiring these same engineers. Although this has created a situation where the company has hired past the theoretical "productive" point, it was still a rational behavior.
Now that the tide is turning, the productivity goal becomes relatively more important than the competitive goal. In the long run though, I don't think the job market will fundamentally change - there is still a shortage of top engineering talent in the US.
In other words, these companies have over-hired as a way to prevent competitors from hiring these same engineers. Although this has created a situation where the company has hired past the theoretical "productive" point, it was still a rational behavior.
Now that the tide is turning, the productivity goal becomes relatively more important than the competitive goal. In the long run though, I don't think the job market will fundamentally change - there is still a shortage of top engineering talent in the US.