Why do people don't just use basic logic?

I am reading in forums for insomnia, a lot of people talk about CBT and if it helps or not.

If the source for your insomnia is poor sleep habits, disturbing thoughts, stress, - then changing your habits through CBT treatment can work.

If the source for your insomnia is physical, neurological, like a brain disease, hormones deficiencies, side effects of medications (there a lot of medications that can cause sleep disturbance) and many other reasons - than changing your habits or thoughts through CBT or any other thing can't help. The solution would be to solve the physical problem.

Like everything, everything depends on the root cause. There are a lot of neurological, physical causes for insomnia, and if the reason then your sleep won't get any better unless you treat it. It's basic logic.