Well, that's an appeal to authority. It also assumes the companies wouldn't be successful with a different hiring approach. In reality the issue is way too complicated to really break down. These companies operate at a large scale and went through rapid growth spurts, and what they believed was a great way to hire was also an implicit tradeoff they were making for the sake of growth.

I'm sure the companies themselves understand that much, and understand a variety of the tradeoffs involved with the way they hire. What they might not understand is that they are at the exploitation stage of their lifespans. There's an entropy-like process as a company matures and cycles through its workforce which leads it to becoming highly specialized.

My bet is these companies don't understand the various ways in which they're limited, and therefore the ways in which they're limited in filtering candidates. And even if they did, they couldn't really hire any other way now even if they wanted to because they don't have the internal diversity for it, that possibility has long since closed on them.