Well as the article stated, the chicken with the teeth did not survive, therefore, it could not have passed on those genes. While the death may or may not have been the result of having teeth, one must survive and reproduce for evolution to occur. Additionally, having teeth must have a distinct advantage if it is to be incorporated into the population. Often a perceived advantage can be a disadvantage. Teeth can be very costly- from the energy expended in production, to upkeep, to fighting off infections.
The same reason we don't have large claws is likely the same reason chickens don't have teeth- they and we don't need them. It does not provide any significant advantage.
Reasonable response.