As I've said, I'm coding and I understood perfectly the code of the devs I was working with, and yet, what OP said correspond to what I have observed sometimes.

As I've said, I'm coding and I understood perfectly the code of the devs I was working with, and yet, what OP said correspond to what I have observed sometimes. This demonstrates that your logic "OP reaches this conclusion, so it's the proof that he does not understand the code, which is the problem" is wrong. If this logic was true, who do you explain that someone like me, who clearly understands the code (I've reviewed it, I've modified it, I've put stuffs in production integrating with their system, ...), agrees with some of OP's considerations? When reading your comment, it is difficult to not be drawn to the idea that you are one of those persons I was mentioning, who are not understanding other employees needs and point-of-view and who interpret systematically any communication failing as "the other person's fault".