+1. Carbon fiber used to be exceedingly expensive, so it sold in limited quantities, but has now become more mainstream in medium range bicycles. Aluminum has displaced steel as the most common material in all but the cheapest department store bicycles, and even kids bikes are made out of it. It's all about manufacturing economics. As far as durability is concerned, I doubt that most people beyond some on this forum worry about it very much. I have never owned a CF or Ti frame, simply because the steel and aluminum frames have worked for me and cost a lot less. I've never had a steel frame failure, and many of my frames are over 25 years old and have been in racing accidents. The only problem I've had with aluminum was a cracked weld at the top of the seat tube on a 1991 Nishiki Alien ACX rigid MTB. If I had wanted to buy a Ti frame I could have done so; I simply don't see the point of spending a lot of money just to get something exotic or for its snob appeal.