At the Univeristy of Texas in the ‘70’s, students called in bomb threats when they had a final they weren’t ready for. But it’s not final time.
We’re in a different era.
In the ‘60s and ‘70s bomb threats were seen as almost harmless pranks—in the same league as pulling a fire alarm (I know it’s hard to believe, given the current environment, but it’s true). A student was likely to get a slap on the wrist if caught.
Today, bomb threats are considered deadly serious. A student would not only be expelled, they would likely face criminal prosecution and even jail time.
In other words, I doubt the recent rash of bomb threats is due to students (for any reason—tests or otherwise).