I think it's great that literacy and the printing press has democratized the reading of books, but when you're faced with such a corpus presented by Catholic tradition, you really need to pick and choose your weekly time investments!
I've inquired with a few religious orders as a layperson. The first thing you will find when inquiring with them is the thickness of tomes that land on the table for all adherents to read. Each religious order has a particular spirituality that is synthesized in the writings of saints and mystics. So if I was not already well-acquainted and well-grounded in the Old and New Testaments, and in the habit of reading those every day, what good would it do me to read Aquinas? Or Leo XIII encyclicals? Pointless.
The Bible itself has so many layers and aspects and messages for us. Many scholars invest entire lifetimes in understanding only the Bible. The only way to be a good Christian is to live the life. It doesn't matter what books you've read, at the end of the day, only your experience and your response to the Holy Spirit. If that means reading books, then good. If that means welding metal, also good. But, don't try to break open the words of Aquinas before you've read Daniel, or Matthew!
Before that the church did expect at least priests and monks and nuns to be able to read the Bible, and there were a lot of them.
Most is strictly true, but you are talking about a millennium between the clear primacy of Rome and the invention of the printing press, and half a millennium since so its not hugely more.
Finally, historically most people could not own books and had no to limited literacy. Literacy is not necessary to be a good anything, but its definitely better to be literate and have access to things to read.