They killed Jedi! But then, when Jango was killed, they had to reuse DNA that led to decaying efficiency or clones. (No idea if its true or not but hey seems viable)

The stormtroopers in the original trilogy are most likely not clones of jango, as the empire stopped using his dna after clones on kamino instigated a small rebellion against the empire. The empire concluded that an entire army consisting of people with exactly the same thoughts and mindset was far too susceptible to corruption, hence the began to use clones from a large variety of templates and began recruiting non-clones into the imperial military force. By the time of the original trilogy most of the jango clones where either, dead or severely crippled by age due to their age being accelerated to twice the rate of the average human, and likely would not be fit for combat service. Only one legion of storm troopers consisted entirely of jango fett clones (the 501st) by the time of a new hope.

Oh neat, thanks for the info!