I wasn't sure if you were exaggerating or not, and by going to
IMDB.com I found that you were not exaggerating, that there were in fact four Air Bud movies. The original only made $24 Million in the box office, so why would 3 more be made?
Kevin Zegers, who plays the kid in 3 of these four movies, was also in a movie called MVP: Most Valuble Primate, a movie about a chimp who plays hockey. And there was a sequel. And there's bound to be more.
Will the unoriginality ever end?
Anyway, to the issue of GB3, there's so much more involved to get a GB3 than there is to get an Air Bud. Why? Oh, I shall list just some of the ways…
-Dan and Co. want cast to be same or similar, at least cameos from originals, while in Air Bud, you can have a different kid and a different dog and no one sees a difference, and it gets released anyway.
-Bill Murray owns part of the franchise, as do several others, indicating a co-ownership. Disney is behind Air Bud and will put out sequels until the day I die or Disney dies, whichever comes first, and with no one else's consent.
-The last point ties in to studio interest, where supposedly Sony didn't want to have anything to do with it, and Disney, once again, will have Air Buds coming out of their noses.
Hope that puts things in perspective.