The main reason students have not been required to buy their own study materials is because no materials have been available to address students' needs.
Interpreter education is very labor-intensive for interpreter educators. In order to maximize your contact time with your students it is extremely beneficial to have all students studying the same material at the same time because it will help you more easily identify student strengths and weaknesses. The high-quality source material can be used in a variety of ways and eliminates the need to search for source material. Exercises are carefully keyed to the source material, guiding you through the teaching process.
Also, by assigning out-of-class study, you increase the student's ability to take responsibility for developing their skills on their own time. If all students have the same study materials for out-of-class use, it can lend greater cohesion to group discussion time, developing study strategies, and insight into their own processing related to interpreting. When students have effective study materials, they can reach their goal of effective interpreting more quickly.
Nationwide, we have a shortage of interpreter education graduates who are fully prepared to enter the job market. By providing students with study materials they can use in the program and on their own as they enter the field, we improve the supply of well-qualified graduates.