It's a problem of the incentives we've setup. We reward engineers for building things. Promotions, pay raises, etc. for engineers are typically based on impact and technical complexity, not how good their documentation was. I've been at a few places that handwave at such things in their level expectations or skills matrix or whatever, but having been in promo discussions at a variety of medium and large companies it always comes down to what was shipped.

Problem is, at mature companies there aren't enough greenfield problems to match the large number of engineers who are looking to climb the ladder. So stuff is rewritten, then rewritten again since nobody understands the rewrite, and so on. Managers kind of look the other way because retention and the ecosystem becomes messier and messier over time as promoted folks leave and new folks come in that need to be promoted.

This is the world of professional software development at pretty much every company not a startup.