What happened with the belts of the Trek District next generation?

Difficult to say a wrong word about the Trek 2nd and 3rd District. They look awesome, and are developed in the same philosophy of the first District: combining retro and futuro elements.













The revolutionary characteristic of the first Trek District was however the belt that replaced the chain, like all bikes have. The belt was inspired by motorcross bikes.

So why not continuing with the belt? What could be the problem with? It is more silent than a chain and there is no grease. I somewhere expected it more frequently intalled on single gear bikes. Fact is however that you have to produce the frame around the belt, and that when the belt breaks, you need to "open and close" the frame, which is the same as destroy it. So the old chain has some advantages.