Why? Because the profs would see to it that they were near-impossible. You'd spend far, far more time, and have far less chance of passing, a takehome/openbook test. Just rip the Band-Aid off and get it over with, was a far better test taking strategy.
Of course, those were in real classes, where we actually earned grades, and had a real (70% or better) chance of flunking out. They weren't "fill-in-the-blank studies", or whatever passes for SJW snowflake school nowadays.
I remember my final in a semiconductor physics class. It was part in-class closed book and part take home. The in-class was relatively painless. The take home took well over a day (24+ hrs) to complete.
“Because the profs would see to it that they were near-impossible. You’d spend far, far more time, and have far less chance of passing, a takehome/openbook test. “
I remember my linear equations class had a take-home mid-term exam that resulted in answers that were 24 pages written. The final was 20 pages written. I would rather have had a simple 2 hour exam instead. Those exams were brutal.