Clio 3 Cambelt Broke, Why ???

Hi. My cambelt broke on my 2007 Clio 1.4 Dynamique, mileage 49k. I now realise it should have been changed after 5 years. it only bent 14 valves which i have now replaced.
My question is about the Cambelt. when i removed the cambelt cover it was full of bits of cambelt. the belt was only 12mm wide ( new one 25mm ). is this normal for an old cambelt. all the pulleys have no movement and the waterpump is ok. of course i will replace all the pulleys and waterpump. wondered what caused it to shred into pieces. dont want the new one to do the same..

thanks

Alex

Clio 3 Cambelt Broke, Why ???