Alex, as best I can tell this change (which has been underway for at least 20 years) is purely from secularization, and it’s now to the point where most undergraduate college students have probably never had textbook that uses B.C. and A.D. A few years ago I wrote supplemental website material for a mainstream publisher’s textbook, and the publisher insisted I use BCE and CE. A few weeks ago I moderated a panel at a conference in which one of the student presenters told me his professor had essentially forced him to use BCE and CE.
The different markers have never really seemed defensible to me because of their inconsistency, i.e. denying that Jesus is special, but still basing the dating system off the traditional year of his birth.