Short answer: Many bolt-on neck joints still have the underside of the fingerboard over the body glued to the top. Taylors do not: the entire neck is a standalone assembly so that changing the neck angle changes the angle of the entire neck assembly, including the fingerboard "extension" over the body.
In fingerboards glued to the top, changing the neck angle doesn't change the angle of the fingerboard extension. The result is that one either needs to make a wedge to fit under the fingerboard extension, or one just glues the fingerboard extension back down to the top, creating a "crease" or bend in the fingerboard at the fret where the transition between neck and body occurs. The bend/crease causes excessive "fall-away", making the string height over the frets along the fretboard extension excessive. If one doesn't ever play in the higher frets, it is irrelevant: if one does play in the higher frets, it matters a lot.
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