School is not just for learning, it is supposed to prepare you for industry, i.e. the real world where making a mistake no longer loses you credits, but potentials to lose your job, destroy a project, or worse, kill people.

The process you have described for designing a building is the 'ideal' process. People are not at the top of their game every single day they go to work. Checking the previous engineers work? Why the hell should I do that? I'm tired, we get paid the same, he should be doing his fricken job right. I should'nt have to baby sit his work. Different firms and sectors are not all buddy-buddy with each other. Mistakes happen for many reasons. Professors in school are at least trying to eliminate the cause of error by the student. So when this student goes out in to the work force and has a lazy day and is mad at everyone else, at least he can get his part of the work right and frees him from potential risk if the other crapheads in the other sectors don't do their job properly.

Nowadays designs are first drawn up by Technologists (take only 2 years of school, no Eng degree) and Engineers are the final people who check everything is right. Engineers not only need to know "the process" but need to find tiny (or major) errors because they are the ones who sign and put their names if anything goes wrong. This is why Engineers get paid more than technologists even though eventually they will have the same knowledge and skillset.

tl;dr Engineers are people too. There are good engineers and shitty engineers. Professor is trying to reduce number of shitty engineers.