The situation in Western Kentucky was "complex & complicated." Kentucky's declaration of neutrality was one factor.
The topography is sliced into north south sections by the Tennessee & Cumberland Rivers. They enter the Ohio only a few miles apart. A short ways down stream, the Ohio meets the Mississippi. East-West movement by land was all but impossible.
The job of defending the Tennessee-Kentucky border was in the hands of one man, Albert Sydney Johnston. Despite the worshipful regard he is held in by some, Johnston had never show any real executive abilities throughout his life. When faced with complex problems, Johnston fixated on one element & all but disregarded the rest. He believed with all his heart that his HQ at Bowling Green was the focus of Union offensive operations.
As a result of Johnston's myopia, Nashville was not fortified; Fort Donelson was constructed on an absurdly large scale; Columbus KY was turned into a massive fortress & the officer's in charge of these isolated fortifications were allowed to indulge in their personal aggrandizement. An already complex problem was made even worse by Johnston's inability to conceive of a coordinated plan & impose his will on his subordinates.
It is way too complicated to go into in this format, but the simple fact is that what would become the cream of the US commanders confronted a collection of dunderheads. Loosing Western Kentucky, which meant loosing Nashville & Middle Tennessee, was arguably a fatal blow to the CSA in the West.
'Army of the Heartland' by Connelly would be my suggestion for the first step in understanding Western Kentucky from the CSA perspective.