The challenge is that sufficiently bad code could be intentional or it could be from a lack of skill.

For example, I've seen a C# application where every function takes in and outputs an array of objects, supposedly built that way so the internal code can be modified without ever having to worry about the contract breaking. It was just as bad as you are imagining, probably worse. Was that incompetence or building things to be so complicated that others would struggle to work on it?