Why does the professor mention volumes of literature?

Listen to part of a lecture in a music history class.
Professor: In our discussions of Renaissance music up till now, we’ve established that when music was copied and distributed to others, it was all written by hand. Can you imagine the tedious nature of that work? Today though, let’s turn our attention to printed music, music that was published through the use of a printing press and we will see that the printing of music actually changed the audience for it, and therefore changed music itself.
    I like to introduce a man named Ottaviano Petrucci. Music printer Ottaviano Petrucci printed his first publications around the year 1500. These were gorgeous publications! They were very expensive to produce, mainly because they required a lot of time and a great deal of precision. Printed music became, in short, a luxury object for the upper class, We know from existing records that for the price of one Petrucci print of music, you could purchase several, yes several, volumes of literature. The revolution in music printing came around 1520 with a French printer named Pierre Attaingnant. The first thing Pierre Attaingnant did was to get an assurance from the king that he would be the only one who could set up a music printing shop in all of France. This is understandable since it was such a risky enterprise, but let’s be realistic, I mean, with no competition, how could he have failed? Anyway, Attaingnant used a new, less expensive way of printing music than Petrucci did. Admittedly, the prints weren’t as attractive as Petrucci’s prints, but they were much, much cheaper and therefore, they actually got used. They weren’t just for collectors to display on a shelf and since they got used, the paper itself degraded and so we don’t have nearly as many Attaingnant prints as we have Petrucci prints.
Student 1: How is the music Attaingnant printed used?
Professor: Well, Attaingnant printed lots of songs, and people were singing them for their own entertainment in their own homes and this use, this amateur sort of domestic performance meant that the musical arrangements needed to be less complex than the arrangements professional musicians would use. This gave rise to a new genre called Parisian chanson. Chanson is a French word for ’song.’ The genre was popular throughout Europe, but still it came to be known as Parisian chanson because so many of the songs were printed in Attaingnant’s shop in Paris. Here is a key feature of Parisian chanson. Imagine you’re standing around a dinner table with three friends getting ready to sing a song that has four different vocal parts. Well, in the printed music book you have, you see only your line of music, only the part that you’ll personally be singing in front of you.
Student 1: Oh, that makes sense. Then you won’t be distracted or confused by everyone else’s pages, right?
Professor: True, but actually having only your part could make it a bit more challenging because you might not know what everybody else is about to sing or even who’s supposed to sing first. Like, think of an orchestra with different instruments. Not all of the start playing right at the beginning of the song. Maybe just the violins start and then the trumpets come in later and so on, but an orchestra has a conductor to tell the musicians when to start, but there’s no conductor in your dining room, so the composers of Parisian chanson worked around this by having all four voice parts start at the same time and in the same rhythm. Now, as the song progressed the rhythms, melodies, and harmonies did get more difficult, more varied, but these songs always had everyone singing the same pattern at the beginning. So, this is a very interesting moment in music history, where it’s very clear that the business side of music, that is to say the selling of printed music by Pierre Attaingnant and those who followed, the business end of music shaped the artistic end. The technology that allowed Attaingnant to produce inexpensive prints affected music itself by leading to the creation of an entirely new genre of music.