Because I remember when my watch, phone, laptop, printer, book, and torch all took a different cable. If I went away, I'd need to pack a dozen different chargers. If I went to a friend's house, I couldn't charge my Nokia because they were HTC people. It having rotational symmetry is nice - but the fact that the entire world of electronics has converged on a single standard is a game changer. When I go on holiday, I take one cable and it does everything.