Star wars: why do stormtroopers suck?

I was rewatching the star wars the clone wars (the cartoon one, not the crappy cgi). and the clone troopers were . i compared them to the stormstroopers from episode 4-6 and saw the huge gap in fighting skills. What happed to them? I played the campaign of star wars battlefront 2, and they said the armor was blasters were supposively better. But seriously what happened to them?