Hmm I think one part every commenter is missing is that students have grown way more mercenary and cynical over the last 20 years. I was shocked in grad school that:

a) I got bullied into sharing my math homework so people could copy it, just like high school and college... but this was math grad school!

b) In 2011 I TAed a 4000-level course where the instructor left the solutions to the homework online (he wrote the book). I estimate 95% of students copied the solutions. It was only 5% of the grade and they paid for it on the exams. Still. Kind of stunning to see at U Waterloo - it was a continuous optimization course and most of them wanted to work in finance, yikes.