It can get worse: me and my teammate trained a new dev for half a year with the explicit intention for him to take over should one of us leave. When the day came, said new dev was moved to another team, the product was given to an outsourcer and I was told to train them how to develop in two 2h sessions before I left. (The product was a legacy mess we were in the (multi year) process of refactoring into something maintainable. Documenting the intentions midway or even the status before was beyond the time budget we were allotted. All of this while doing feature development, without having proper requirements or user stories or access to customers who understand their use case, of course.)

That's exactly my point. If companies aren't expecting their developers to document their services - while the developers are still employed and building those services in the first place - that's a failure in my books. It's exactly the sort of corporate culture that props up this mindset of "promotion-driven development".