2. Laziness. This is the "unwilling" of the "unwilling or unable" scenario. Of course, there are other reasons, but as a writing enthusiast, it bothers me that
the writer(s) can't be arsed to come up with an explanation. It should be noted that there ''is'' a difference between mentioning something offhandedly and never exploring it, and deliberately withholding a crucial piece of the plot because the writers think it makes them look clever. And the truth is, it just becomes a whole bunch of wasted effort that would have been better put to use elsewhere.