Adam said it on Twitter, when everyone was all bitchy about MLG. He said it's not about profiting, he feels MK (Fighters) are great, and they want to help build their community because the gaming community help build MLG.
Fighting games are on the rise in popularity. They are also far easier for a casual viewer to watch and understand compared to RTS, FPS, and MOBA's. I think MLG is trying to get in on the ground floor, because fighting games will eventually be the top grossing esport (so to speak).
Let's face it, MLG is not a charity. Hell, I've heard rumors that they are underwater financially. They are trying to make money and they are looking toward the future with their decision to bring fighters back.