The reason is most people can tell red from green and big from small, and most people use graphic designs daily, so will have an opinion on whether a design element should be bigger or redder.
Other professionals with a similar plight could be copywriters, and devs when selling a PR.
I am a professional graphic designer. Presenting with obvious defects to fix before shipping is not common practice. In any serious design engagement, the client would probably just be confused about why something changed after approval and it would lead to an unnecessary meeting. On top of that, I'd probably end up having to revert to the shittier version they agreed on and waste time re-packaging the deliverable. Purposefully using up contractually allocated revisions with deliberate flaws, while very difficult to prove, is essentially fraud. If the graphic designers you patronize do that, get new ones.
The reason is most people can tell red from green and big from small, and most people use graphic designs daily, so will have an opinion on whether a design element should be bigger or redder.
Other professionals with a similar plight could be copywriters, and devs when selling a PR.
Compare to plumbers or lawyers.