I'm not sure if it is really simple sometimes. Our class only has about 2 dogs (Riley and his BFF Jamie) left from the original 8 who started a year ago. Now most of them were the owners deciding that they did not feel like continuing, but there were a few interesting dogs.
One (a golden doodle) was not motivated by her owner AT ALL to play the game, so she would run off or try to play with everyone else rather than do the equipment. She would work beautifully when he actually rewarded her with her ball, but he was not consistent about encouraging her to love the class. They quit agility, and now Quinn is excelling in nose work and obedience. (Exactly the lack of owner motivation/arousal you mentioned)
The other one was a little Aussie. She was a very 'soft' dog whose owner was very gentle with (she only needed a stern look as a reprimand EVER). She was doing great in agility UNTIL we started doing more off leash work. Suddenly the dog would run and hide under a chair, or roll over and lay there completely shutting down. The owner tried everything, including some really awesome treats to get her to work even over just one fence, but nothing. She would do the jumps and go thru the tunnel with her tail wagging is she was on leash (and get super reinforced), but shut down off leash (and she was an experienced rally o dog who could perform off leash with no issues). She loved the other dogs too, so no fear issues with them or the people. They quit agility and stayed in Rally....where she will do the jump off leash with no issues????
Like with everything else, I won't give a definite that 'all dogs' will love agility; no, I've seen my share of dogs who don't want anything to do with it or do it because their handler is asking them to perform even though it's not their favorite thing to do.
Why would a dog be fine off leash in Rally versus Agility, who knows. Maybe it's sounds? Maybe its atmosphere? Maybe it's that the dog doesn't enjoy the activity.
Yes, I'll agree that SOME dogs don't enjoy the sport but I
will not agree that just because a dog shuts down or refuses an obstacle they don't like the it. There
could be other issues, such as those we've already listed, at play.
Heck, if you watch CJ run, it would be just as easy to mark her with the same stamp Sharon is using here for 'all dogs who refuse to play'. BUT if you watch her, she grows in confidence and you can see the joy in her body language. And in training, she's so full of energy to play and interact with Glen that she even sasses him when he doesn't give her the correct instruction. We'd have missed all this joy with her if we'd have given up early on and assumed she 'didn't like' agility versus having to build her confidence.
Sorry, I can't agree, without knowing the full story behind this dog, that it simply doesn't like agility. Could it be true, sure; but it could also be true that the dog simply needs more time. Either way, let the dog and handler have their time together. The life of our companions is too short to dictate who can and can't play certain sports with their dogs.