The reason GPS wants you to take 150 is that it is the "most direct" route. That is, 64 goes east to Lexington where you get on 75 to head south. That makes 150 the hypotenuse of the (rough) triangle which, as the crow flies, is usually the shorter/faster path.
What GPS doesn't take into consideration is all the Podunk little towns and traffic controls that slow you down.
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