I've noticed that some publication venues add the degree type links to the author name, like MS, PhD, MBA or MD. What's the point? (example)
It depends completely on the journal's editorial criteria. Some journals will expect that the degrees are included (see JAMA) and some will not (see Research in the Teaching of English). Professional ego will not come into it -- the journal will want to maintain uniformity from article to article.
Academic cultures differ as to whether degrees are typically appended to names. In the academic culture in which I spent 30 years of my professional life, use of the "Ph.D." was seen as unnecessary -- if one identified oneself as "Associate Professor of English" or "Professor of English," the Ph.D. was assumed.
I cannot generalize, based on your single-document example. There might be various reasons, such as publication outlet's requirements or authors' professional ego (see egocentrism and/or egotism). However, in that particular case, it can be argued that the degree attribution has been done to clarify that some of the authors are not Ph.D. holders. Not that it matters much (or should matter much or at all, that is), but, perhaps, the authors wanted to be more precise in attribution in order to prevent confusion due to implied assumption that all authors are doctoral degree holders.