Very few of them have worked on a single system for more than four or five years, and have no idea what their decisions cost after they left. Many have joined a project after four or five years and suffered from those decisions, but they don't actually know why the decisions were made - how things looked at the time those decisions were made - and so they can make the same mistakes in their next greenfield project.

Of course, some systems have to ship at all costs or there won't be a second or third year, so judgement is still required.

But a lot of experienced people still underweight the costs of having lots of "low impact" defects.