McKay becomes a really nerd genius on Atlantis... I hope that at least write some books about what happens on Destiny before they got to sleep.
In one of his first appearances on SG1, he invites Carter to the cafeteria, mentioning that they have lemon chicken, with excitement. If I'm not mistaken, it's not until the SGA fork that he seems to be allergic to citrus.
...I'm really embarrassed that I know that from memory.
My own supposition is that it's the standard rights-squatting thing a studio does when they're done producing a given work and don't want to compete against 'their' IP being used by someone that actually has a good story to tell.
All of them failed. I really don't know why MGM didn't gave it to a AAA studio, such shame...