You're right that reading code is harder than writing, but I think your statement is too extreme - it implies crap code does not really exist or everything is crap. However, we all know that only 90% of everything is crap.
Personally I maintained various codebases (not written by me) and some of them were really terrible, utter mess, while some others were pretty nice to work with, even if I had to refactor sometimes. If programmers thought about code design at least for a while before writing it, and then the code is well-organized (= good separation of concerns, no global state, no copy-paste, complex parts isolated from the simple parts) - it doesn't matter that much that they didn't think of a new feature you're now adding to it.
Personally I maintained various codebases (not written by me) and some of them were really terrible, utter mess, while some others were pretty nice to work with, even if I had to refactor sometimes. If programmers thought about code design at least for a while before writing it, and then the code is well-organized (= good separation of concerns, no global state, no copy-paste, complex parts isolated from the simple parts) - it doesn't matter that much that they didn't think of a new feature you're now adding to it.