Our Amstaff gets walked twice a day, played with all the time and comes inside/outside - but she is just FULL ON! Hardly sits still, she is also a pup so I guess that doesn't help
It's simply because they are different breeds. Kelpies are bred to work... and work hard. While English Staffies were originally bred as farm working dogs, modern English Staffys, the American Staffy and the Pit Bull have all been bred to different temperate requirements and have become predominantly companion dogs.
Kelpies are still a true working breed. That's the difference.They are both hightly intelligent breeds though.
I'd think about chatting to a reputable dog trainer, dog behaviouralist or contact the Kelpie club. They'll give you some great info on how to target the specific Kelpie behaviour problems.