Scott Kelby is successful...Scott Kelby is a businessman...shocking.
You see, it's a bit like when doctors recommend a certain drug and then you discover they were taking money from the pharma company. Maybe they really believe the drug is great and being sponsored by its manufacturer has nothing to do with their professional opinion... but you'll never put the doubt 100% aside.
We're certainly not a that level here, but in a way I believe many people felt like Kelby's economical interests did get in the way of his photographic recommendations in this situation. Might be the theatricality of the whole thing.
One thing that seems to get lost in this discussion is that Scott is NOT recommending that anyone switch to Canon. As a fairly high-profile camera person, he has been asked repeatedly why he made the switch, and so he decided to put together a video explaining that so that he wouldn't have to keep answering the question over and over. Whether you believe what he says, or whether you take it with a grain of salt, is YOUR decision. Personally, I have too much invested in Canon gear that I've acquired over the years to even think about changing, especially since my camera gear far exceeds my talents. But the photographer who shot my daughter's wedding 9 years ago switched from Canon to Nikon (prior to the introduction of the 5DIII and the 1Dx), and is perfectly happy with his choice.