In defense of the instructors, such as tenured/tenure-track professors and visiting/adjunct professors, and teaching assistants (T.A.s), it takes a lot of work to create/update a set of presentation slides, lecture notes, laboratory/lab assignments, and course projects for courses on computer architecture, or even their requisite course on computer systems. This has to be done in addition to preparing for the lessons that they teach (or lectures, if you like), lab sessions that they manage, and ...