I'm a game developer. I know how this works. Keep in mind, what you are saying is very true. Pokemon will sell boat loads despite the quality of game it is. As a game developer, my first job is to make a great game. My second job is to make money. I think this way and I know for a fact that many other game developers do the same. You can tell when there is a lot of love poured into a game. Skyrim, for example, has tons of love in it from the quirky quotes the massive numbers of easter eggs. Pokemon has very little love involved. Let's look at movies. Scott Pilgrim Vs the World was "perfect" according to the director. He was VERY happy with it, but it effectively flunked in the box office. All of the fans that saw it LOVED it, but it didn't make money. Nobody was unhappy with the movie, but it effectively flunked by most metric standards. The converse of this is also true. Look at rottentomatoes.com. The top movies right now aren't good movies. They make tons of money. The goal of the developers is to make a good product. Pokemon sells well, so why innovate and try to change the game too much? That could be financially dangerous. As a result, the developers have been told to not innovate. Same goes for other series such as CoD. CoD releases the same game every year but with a different coat of paint. People still buy it, so why innovate?
No matter how bad a Pokemon game is, it will sell. Look at PBR. That was barely a game, but it sold huge amounts. The Pokemon logo carries a lot of weight. Platinum was barely an update to DP and Emerald was barely an update to RS. I'm fully expecting BW2 to be a minor update to BW. These "updates" are very lazy and the professional gamers are noticing. I speak from experience. Previous games have been lazy updates, so what makes us think that the future one will be any different? Why rerelease the same game with minor updates? Money.
The goal of the game developers in this case is to mad off the least amount of people. X or more people will buy the game no-matter how good it is. As long as I don't change the formula that much, I am certain to get that X many sales. Actually trying to create a new game would make that number of sales questionable. Why innovate when I am certain X sales? Money.