Some people just make stuff up to fit a story they want to tell, like “Cs morph into S” with no evidence this happens or is even possible. In college you are taught not to manufacture evidence to fit a preconceived story you want to tell.
I think a lot of grad school bound students likely do not do S/NS in their major, and many grad schools are more concerned with gpa in major or last 2 years than overall gpa.