First, you're certainly lucky. Secondly, the emphasis should be on "by default"; managers can, and some easily and quickly do, prove that they aren't adversaria

First, you're certainly lucky. Secondly, the emphasis should be on "by default"; managers can, and some easily and quickly do, prove that they aren't adversarial. But companies (especially tech companies with high stress on unsustainable growth) don't often incentivize that, and sometimes disincentivize it whether they mean to or not.