Jaroslav Peliken writes knowledgeably on this.
Including the books doesn't mean they were always cosidered to be inspired. And I find it interesting how you disregard the first centuries' take on them; usually catholics would count the early fathers' opinions as sacrosanct.
It's usually only the spur of dissent or the pressure of controversy that motivates the forensic "defining"
I don't know about "usually". But in this case it's the Biblical content itself as well as other external factors such as the Jews never having considered the apocrypha as inspired (for good reason).
It's good history...not inspired.