The other is your hand would occlude what you wanted to see, and the third, which was the winner, was that your fingers would get the screen dirty, and hence, fingers would never be a device that you'd use.
Zweitens verdecke die Hand,  was man sehen wollte, und drittens -- das Beste -- würden die Finger den Bildschirm verschmutzen. Und deshalb würden Finger niemals das Mittel der Wahl werden.