Well, yes and no.
He didn't connect
Ender's Game and
Speaker for the Dead for commercial reasons, since they appeal to different audiences. The reasoning was artistic. Who better to be the speaker for the dead than the child that commited the Xenocide? Indeed, who else could have the right?
Speaker for the Dead left a lot of open tensions at the end. Eventually, Card wrote several sequels. There was nothing too commercial in his intent here, as OSC fans tend to be OSC rather than
Speaker for the Dead series fans (if you read the series you'll understand why--which is why you should read some of his other work first
).
Then he was approached about having another writer do some more battleschool stories. This was commercial. Card didn't want to write any more "kids in space" books, at least, he thought he didn't. So he started to work with this other author that would be writing books about battleschool.
And Card realized, thinking about it, that he
did want to write those stories himself after all. So he snatched the project back, revised the concept, and set to work.
I guess you could say something about the artistic integrity of having the original writer write those books or something, but Card admits that he was just being selfish. He wanted to write those books himself, and since he hadn't signed the dotted line just yet, he ran with it.
So he wouldn't have revisited the Battleschool if it hadn't been for the fact that there was a commercial push behind it, but he wouldn't have written them
himself if the idea hadn't attracted him all over again as an artist.
I don't know of anything that Card has written "just to pay the bills", come to think of it. And he does a fair amount of his writing gratis. He's one of those "I'm gonna change the world" types, I guess (read
A Storyteller in Zion sometime to get an idea of how radically he wants to change the world--if the title doesn't say it all).