I think the lack of tests was more symptomatic of bad incentives that good developers were forced to follow. Developers were rewarded for flashy things they could show promo committees, and rigorous tests or well-written documentation.

It was unusual to find code with no tests because a code reviewer will usually insist on at least some tests. But it was common to see complicated behavior with just a single test associated. Or a complicated interaction between components with no end-to-end tests.

There's not really a strict cultural expectation for documentation, so it's very easy to find code that's either not documented, documented inaccurately, or documented unhelpfully.