Keep in mind that in the Anglo-Saxon period, books were entirely written by hand. And the most demanded book? The Bible, of course. And there was the need for other Church documents, from copies of prayer, to declarations from the Pope, and so on.

Other documents likely were at best, "back burner" items. The Church didn't particularly want to preserve pagan stories. (Beowulf was obviously given a Christain facade--always wondered why the monk chose to preserve a pagan story, to be honest...)There are only so many trained clerks, so many hours in the day