Getting back to the original question, it may have something to do with not having an ear for such things. I know someone who reads the dots extremely well and can play a number of instruments. However, she is completely unable to work out the chords by ear for even the most basic tune and cannot play said tune without the written chords before her. This person loves music and loves to play it; but appears to be incapable of hearing chords well enough to suss them out for herself. I am sure she is not the only one.