Scribes and Scholars is a fairly dense academic book that covers how ancient Greek and Latin literature was transmitted through the centuries. For what it is it’s a pretty solid book and is clearly thoroughly researched.
Antiquity
With early books contained on scrolls (and somewhat rare on top of that) they weren’t particularly easy to use. One hypothesis for why there’s often such a substantial difference between two versions of quoted text is that ancient authors quoted from memory rather than go through the effort of finding and unrolling the text itself.
One of the greatest contributions the library at Alexandria made was to the standardization of texts. We see variation in earlier versions fade away and consistency rise. In the case of something like Homer it seems that scholars had settled on what the accepted version of the text was.
Scribes relied on marginalia notes and symbols to denote certain things. An asteriskos, for example, marked a verse that was incorrectly repeated in another passage.
Educational texts of the Middle Ages often relied upon works from antiquity. They’d rely on ancient authors to illustrate concepts and teach students.
Classical scholars owe a great debt to these abridgements and commentaries, grammars and handbooks, for they have preserved, even if at second-hand or in fragmentary form, a very considerable amount of literature and learning that would otherwise have perished.
It seems that the impetus for changing the format of the book came from early Christians. While the pagan codex was relatively rare it, at the same time in history, was universal for biblical texts.
The Greek East
In the early Christian era many of the Classical texts that were lost were lost not due to disagreement or conflict, just lack of interest.
one of the major reasons for the loss of classical texts is that most Christians were not interested in reading them, and hence not enough new copies of the texts were made to ensure their survival in an age of war and destruction.
They did have a limited place in schools and were not widely censored nor destroyed. Constantinople, though, was the center of this literature preservation. The 13th century was devastating for it, though. The sack and destruction of the city, while materially less than that of the 15th century, had a greater impact upon literature and many works were lost.
The Latin West
With the decline of the Roman Empire books came to fall under the purview of the Church. Classical works had a tenuous position here. But when it comes to the craft of bookmaking nothing had been lost and the Church remained capable of producing stellar work.
An important result of a rapidly developing and highly organized educational program, spreading from the court to the monasteries and cathedrals, was the need for books; these were produced on an unprecedented scale, in a flurry of activity which salvaged for us the greater part of Latin literature.
The development of Carolingnian minuscule, a script developed to ease the administration of Charlemagne’s empire, had a secondary result in making books easier to read and work with. This likely made books more likely to be copied as well.
Even this relative revival left things in an often precarious place. For example:
There are some extraordinary examples of survival: the fifth-century manuscript of Livy’s fifth decade which found a home at Lorsch (Vienna lat. 15) survived until the sixteenth century without ever being copied. A mere mishap, and five more books of Livy would have disappeared without trace.
The Renaissance
The humanist movement renewed interest in Classical books. And the printing press enabled books to be copied in greater numbers than during the scribal days. The problem is that,
Once they had carefully copied a text, they were liable to have little interest in the manuscript which had preserved it.