It really is a lot more trouble to input the tune into abc software than it is just to read it--As to your comments about sight singing--it is not a particularly difficult skill--kids in school choirs learn to sight sing, and we used to teach the orchestra kids to sight sing their parts in preparation for sight reading competition--and orchestral scores are way more challenging than the melodies from songbooks are likely to be.

To turn your analogy around a bit, some folks want a computer program that lets them perform brain surgery,without having to learn medicine--