Would you be able to elaborate on why they dropped out? did they hit a point where cheating wasn't possible? or maybe realized it was pointless and unhelpful once they need to do a job?
Some students ignored his rants because they didn't find the subject interesting, did the past papers, and then got to the exam and did terribly, then complained about the fact that "it's all based on his rants".
Others found the ranting engaging because it was deep dives on obscure bits of computer security history. My year he spent ~4 weeks going on about Stuxnet, including deep dives into the wider political context. When I got to the paper, one of the few questions we could choose, for 50% of the paper, was just "What was Stuxnet". I wrote pages and pages. Figured out from marking that I got full marks on that one. I always did great in that lecturer's modules despite never taking notes and rarely doing any targeted reading.
To show the level of engagement, I once turned up to one of these lectures 10 mins late, with most of the class already there, and the lecturer said "oh I wondered where you guys were, I guess I'll start again". He knew we were the only ones who cared about the class.
As much as it sounded like the rantings of a tin-foil hat wearing madman, he was in fact quite accurate through a combination of having worked in government in computer security at a fairly high level for a while, and having deep technical knowledge about what was possible.
I miss his lectures, they were excellent, but I hear he's still going strong scaring freshers and running the on-campus teaching union, which is nice to hear.
The path of being interested enough in a field that the easy work is easy, and the hard work is at least interesting, actually turns out to be the path of least resistance.