The problem being a dev at a big company (around 1000 devs) with huge codebase (I mean huge, tens of thousands of modules, if not millions) is that, as many hands touch the code of a project and deadlines are always short, not everyone care about changing the documentation afterwards.

This translates to double the work everytime you need to fix a bug or something as you have to quickly reverse engineer the modules to understand it - the documentation often reflects an old version and it messes things up much more than it helps you out.

Even worse is when there is no documentation in some subsystems - it is all over someones head, and if the company fires this guy you have no one to resort if you have to touch his code. That is frustrating

Management should address this issue. Maybe dedicated resource to help with proper documentation? Seems it would have major ROI. Thoughts?

Proper comments should be looked at as well as code during the review process. I always do that. It annoys some people but it's necessary

I work at a company from the finance sector, $50b in revenue.

The IT sector there is massive, ~1000 devs and over 4000 of people supporting operations, project management, infrastructure and so on.

It is very hard to put code into production, a lot of gates to check code and documentation to hold back potential issues, nonetheless there is still a long way to improve code quality and documentation.

There are header comments on every program though, and it is a good practice to indicate what you are changing in your version. You can also tag the lines you have changed to simplify posterior checking, but, for instance, if you are a new dev these comments don't help much.