I see your point, but Mortal Kombat is not really the best example of a cash-cow franchise that keeps selling the same game over and over. The successive games in this series have huge differences, especially since the reboot a few years back. If you like this style of fighting games, there are plenty of reasons to buy the latest version every few years.
FIFA on the other hand is terrible in this regard. I can say with confidence because I've been buying each entry since FIFA'09, and while there have been a few major changes in 10 years that are worthwhile improvements, you are indeed more or less buying the same game every year. I sometimes wonder why I even keep doing it, I guess it's just because it's become a tradition I cannot get away from, getting the game on release date and inviting my brother to play it until deep in the night.