Derek has an interesting post here on early medieval liturgical materials. As Derek points out, to do the daily office in the early medieval period required juggling five different books — breviary, collectar (with collects, I presume?), psalter, antiphoner, and hymnal. How many clergy would want to juggle this many books, much less laity? Besides, this requires a mini-library and is not very useful for travel. Books of hours then provided primarily the laity with one book that contained everything they needed to pray the hours.
Now to be sure, some of the above books may have had a combination of materials in one book, say psalter and antiphoner or hymnal. Indeed, psalters were the most multifunctional early books, usually containing additional matierals like liturgical calendars, antiphons (sometimes in place before and after the psalms), and a collection of other prayers. Likewise, breviaries contained a wide variety of material and are the clerical version of a book of hours. As the liturgy became more complex, breviaries got not so brief, and became difficult to handle.
I think its a shame that antiphons have been largely forgotten and collects have become rather cookie cutter. I hope to post some new collects here in time.