What tends to happen on bolt-on versions of set-neck guitars is that you don't have enough thickness of wood to keep the same neck angle and height above the body, without making either the neck, or the body cutaway for the neck, too thin for a solid, safe joint. So the neck angle (which on the set-neck will give you the required string height above the body at the bridge) is decreased or removed completely, and the required string height at the bridge obtained by having the fretboard sit higher above the body - which allows for a solid neck and heel joint.