It used to be pen and paper, maybe a slide rule. You couldn't cheat except by bringing in extra books or papers which were easy to detect.

Then they allowed electric scientific calculators which were checked prior exams. You could theoretically store some meaningful constants in their memory but it wouldn't have been very useful.

Then laptops... what a can of worms! Even making read-only terminals available for students during exams would open up loads of potential holes for cheating. But that's nothing in comparison to private laptops. Even private laptops booting the school's own USB images would be highly untrusted but letting students run their own software and hoping school staff to find any problems by inspecting them is, from the policy viewpoint, just going bananas.

In fact, if I were a non-hacker student I would oppose strongly to the whole idea because I could be certain that at least some of my peers would be using their laptops to hack themselves an advantage over me and most others.