I sometimes describe programming as a one-way hash operation on requirements. A lot of information and context gets lost when writing software, and I haven't seen a workable solution to that problem yet.
This is closer to the root of the problem than saying code is unreadable... the information isn't lost because of the code being produced, it's lost because the developer leaves. Documentation won't work because requirements change faster than they can be documented. I don't know a solution other than just trying to convince that developer not to leave.
IMO that's part of why readable code is so important. If I can look at a piece of code and understand its behavior then I can know something. I might not know what stated requirement it was trying to solve, but I can know for sure what requirements it implements.
Compare that to sloppy code bases with side effects everywhere where you don't know what it's supposed to do or what it does.
