Musicians ship instruments to luthiers (I think), woodwind repair people, and the like all the time—I do, at least. But the issue if traveling by air is, if you're asking why don't we just ship to destination with the 24+ hours that takes, you might as well ask why don't we drive to destination X. Many musicians log plenty of road miles, too....if you're flying, you need the instrument on both ends of the journey for practice/rehearsal/performance, so onto the plane it goes.