I play worse things than guitars to tune and there's always the problem of other people's tuning to be taken into account. What's the point of having a perfect concert pitch guitar, mandolin or whatever, if it isn't in tune with the box? And to retune a box involves a lot of screws and bits.... (By the way there are worse things than mandolin banjos to tune - there are lutes with moveable gut frets, and sitars and other inventions of sadists...)