Exhaust Help

Hey everyone I need someone to help me out with some exhaust questions I have. I really like the sound of JBA's full exhaust set up (JBA long tube headers p/n-6675S + JBA H-pipe p/n-6675H +JBA exhaust systen p/n-50-2627) But all the parts say for off road use only, even the catted H pipe version. What makes an exhaust system not street legal?
Thanks for any help!

Thats what I thought! I was just confused when the catted H-Pipe said for off road use only on JBA's website, but thanks alot!!