Grant is/was a child actor, and this show is nothing new...aka reality tv series. Look Grant up, he has been in a number of things as a child (Eight is Enough, etc.). This is a casted and scripted television series...reality or not, it is casted and scripted.
I hate to burst everyone's bubble, but it is what it is. He is either being truthful and leaving to be with his family, or even more typical, a contract dispute that was never resolved. Grant is probably taking his "ball" and going home. At a certain point, the marginal cost will out-weigh the marginal benefit...aka...not getting paid or benefited enough to put up with this crap anymore.
I enjoy the show....I just know it is excellent scripted and well written for "entertainment purposes only" scenario. I wish Grant and his family the best of luck, and hope he has thought of the tough job market economy...even for actors
If you're a fan be supportive and stop speculating about what you don't know, if you're not why do you care? Just appreciate all the good work done over the years and say good-bye, good luck and please visit now and then.