How can one rely only on ingredients?
All of these chocolate bars are made on multi-million dollar machines that are hot (they melt the chocolate) and some of the company products may have real treif in them (gelatin) and if there is no hechsher, while this product may have no treif ingredients, it could be BOSSOR B’CHOLOV!! (Non-kosher gelatin and milk chocolate!!)
If there is a hechsher, obviously the machine is kashered in between (we hope), which takes time and money and therefore cost the kosher consumer more.