Well not using psychological reasoning here, more common sense. Some people are perfectionists, such as my handwriting (an error is approximately every third page) ant it is super small. I prefer my handwriting to others.
Some may be more inclined to buy new text books as it allows them to be able to start anew, highlight sections for their understanding rather than another's highlighting, etc...
Also most sensible people don't like buying second hand textbooks with crude drawings in them.
However I'm not saying its not a bad idea to check out second hand book sales. There is always the possibility that you can pick up something good. Also year elevens should ask finishing year 12's if they can buy their text books. I for one have a large number of English textbooks (thought it might help but errrrr.....), and I'm passing it on to my best mate (possibly going to be the dux of our school next year

) so he can get into computer science.
Any more questions, just ask.