Many coins are designed by geocachers, but some are designed by the shops, too. And some cachers have their personal coins and there are many places, where coins are made
I can't really say something about the motivation to make a coin, because i haven't made my own yet.
But i love all the coins i own and because of that i keep many of them at home, because it would nearly broke my heart to see them go missing.
But it's a great feeling, too, to see a traveled coin come back to you
Unfortunately many coins go missing, because caches are muggled or some inexperienced coiners keep them, cause they don't really know what to do with them and how to log them.
Hope you can understand my english