The short answer is that it is just for dramatic license. They likely could in real life.
Keep in mind that the point of the detonator is to produce a charge large enough to cause the compound to detonate (otherwise, depending on the compound, it may just slowly burn; it can actually be used for warmth in a cold environment), so it would still be important for it to not be close to a part of human anatomy when it goes off.
In movies when they have bombs with C4, why can’t they just pull the detonators out of the sticks of the explosive blocks?
A terrific video on the chemistry (to fit the requirements and geology of the site), measurement (mounting into a large, heavy pendulum, and then measuring the swing), and construction (distributed as large, sausage-like packages) of commercial dynamite:
Visit an explosives factory and learn about nitroglycerin
Pictured is an explosion in a military context. The pictures of military explosions are decidedly more entertaining than commercial ones.
What? How? Wonder. 