Why do you think explosives is the only tool of the trade for terrorists? But even for bombs, it's "beneficial" to have understand reliable detonation mechanisms, blast radii, shaping, and weight. And questions like "will this bring a building down or not?" or "will x-rays detect this?", or given that not all terrorists are suicidal, and not all targets can be approached at pont blank, even "how far away does a person need to be to survive the blast?"
For non-bombs, trajectories can be important. Or fuel rate consumption. Or counterweights.
I can fully see those who train terrorists sending some of them off to engineering schools. That likely has a higher payoff than, say, culinary school. And given how rare it is being a terrorist, it shouldn't take many to offset the statistics in the reverse direction.