Tech companies have a bias as to what universities they hire from, which when coupled with people recommending others they know, results in a reinforcing policy.

I am aware of people and execs who would preferentially choose Ivys and the big private schools, sometimes even specific schools (e.g. Stanford grads). Given the high end schools have also historically been super racist (e.g. explicitly banning black people entirely until that was ruled absolutely illegal), and still maintain that racism after that through a bunch of subtle mechanisms - for a number it's still seemingly deliberate.

It should be fairly clear how in that environment it is necessary to explicitly pay attention to who and how you're hiring in order to avoid simply reinforcing and repeating existing biases.