A number of things could arguably get a student easily bored when reading and I'll try to highlight the ones that first come to mind:
(1) LACK OF INTEREST IN COURSE OF STUDY: I'm treating this as a question about students in tertiary institutions, so I'll just say it could result from them not totally loving what they do in school. The course may have been chosen for them by parents or school so in most cases, they study with spite for said course.
(2)STATE OF MIND: A student could have the willingness to read but get bored because they are bothered about a thing or two or are just perpetually sad. In this case, there might be a problem needing just more than motivation as a solution.
(3)UNSERIOUSNESS: This is more than half the time the problem students have, but would mask it to seem a couple other things.
(4)LACK OF MOTIVATION
What makes students bored while reading books is the fact that they are not serious students. They have not tuned their mind to studying and coming out of school with flying colours.
Studying is something one must determine to do, when you force yourself to study it becomes boring. When you have set a goal and you know what you stand to gain if your goal is accomplished then you don't have cause to see studying your books as being boring.