Someone's bio might appear in how many articles? A few hundred? And how often will the bio be updated? A couple of times a year? So, updating a bio comes down to touching a few hundred records a few times a year. Compare that with thousands of accesses per day and you've suddenly tipped the scale.
That would make sense if you had to pull bios with an article, which should hardly be the case. At most, you'd have to pull in current authors' affiliations. A bio would ideally stay behind an author link, and be pulled in quite rarely. I for one would much rather have a list of authors immediately followed by the abstract than having to move through several pages of biographies for an article with 4-5 authors in order to find the abstract an the actual article. So for me the decision to put every bio in every article looked like a poorly researched one. YMMV and all that.