Here we have a typical Hollywood bomb, which is featured with relatively minor variations in hundreds (if not thousands) of titles:

However, just looking at it, I’m confused. Why are these bombs supposedly so difficult to defuse? It seems like the hero could just pull the blasting cap out of the explosive, or cut the wire to the blasting cap. Instead, they always seem to struggle with cutting the correct wire to stop or disable the timer. But who cares about the timer if it’s no longer connected to the explosive?
I know without naming a specific title it’s hard to give an in-universe answer, but is there some out-of-universe answer, such as directors (or at least prop designers) universally not caring whether their bomb scenes are remotely realistic? Or is there some sort of agreement to show only stupidly-built bombs so that amateur terrorists will include this obvious flaw and make real bomb squads’ job easier?