to some, time is not money; paper is.

student effort has many means of measurement:

• i've seen many students spend hours and hours at the math help desk, working out all the homework problems as tutors start and end their shifts.
  
  some of my students look sleep-deprived. the programmers in the group look "screen shocked" -- that is, the dull, sleepy look that comes from staring at a screen for too long.
  
  
• on the other hand, when looking at their write-ups, they are miserly with paper. they seem to make a "budget" in advance, say 1/3 or 1/4 of a page, per problem.
  
  if the work for the problem exceeds this quota, they may very well choose not to do the rest!
  

my only conclusion is that, for most people, time is not easily or actively measured in cost, so it is easily wasted. on the other hand, a new notebook has a visible price tag. let's give them the benefit of the doubt: maybe they are environmentalists and want to save trees! (: