You also have to take the Dunning-Kruger effect into account, where most developers aren't able to evaluate themselves correctly. In our work we have a tendency to view thing as "right" and "wrong". I often find people with a few years of experience to be the worst. They have enough experience to recognise that they are more knowledgable than juniors, but lack the overall picture.
Some even come out of studies this way, because they are used to being the smartest in their class and have built up their egos. "Why is the old shitty code written this way, they must have been stupid? We need to rewrite it in the framework I read about in the blog last week". Only experience will teach them that things are not that simple. If they are not exposed to the right working environments in their first jobs, they will spread this negativity for years until they (hopefully) grow as persons.
Pro tip: If something looks unnecessarily complex, there may actually be a reason for it. In the case where you need to rewrite/refactor working stable code, don't try to negatively push down others to enhance your own feeling of superiority. Keep the arguments as objective as possible. If you have tracked the code to specific individuals, at least talk to them in private first to get their input instead of assuming you know best.