Don't let the complexities wary you too much! There is clearly a connection between the biblical odes (which were in usage first; drawn from the scriptures), and the canon(s) of odes that are in fact direct reflections on the themes of their associated odes from the biblical set. During the weeks of Great Lent, when the biblical odes are read together with the canon, this becomes very clear: the biblical odes are the 'root'; the canon (or, properly, multiple canons) are intersperced with their verses, oftentimes reflecting directly on what is being said in the scriptural song.
How and why and when Ode II dropped out of common usage, except in Great Lent, to such a universal extent that canons are henceforth not even written with a second ode, is a phenomenon of liturgical history about which I cannot offer any insight. The most commonly-offered response to the question is that its imagery is 'too grave' for normal usage; but I have never found this either satisfactory or accurate (not satisfactory, because grave imagery is not a thing to be shied from in liturgical song; and not accurate, because there are liturgical texts in regular use in the service books and menaia which are far more grave in imagery than the second biblical ode and associated odes in the Lenten canons). There must be other issues at play -- but I am not a liturgical historian, so could only guess at this.
INXC, Deacon Matthew
Thank you Father Deacon,
To be clear, when you use "Ode" in the post quoted you are using this word interchangeably with Canticle. Correct? In other words, by "Ode" you are referring the scriptural excerpts, not the extrabiblical hymn (which, if I understand your words, is based directly off of the corresponding Canticle).
Please correct me where I err.
PS: I don't want you to think I am losing sleep over this. it's just that in understanding patterns and purposes I am able to more easily address more meaning to what is otherwise a very confusing and random set of prayers and hymns. Indeed, I am losing sleep, a lot of it, but that's due to my teething 11 mo old