So they can have a massive disco party, based on their looks.
But all joking aside, I think that the money goal is really a cover-up for something even bigger, having to do with DNA and the legendaries. What I think is that they captured two Pokemon, Sawsbuck and Noivern, to experiment on them, by modifying their DNA sequence, just to see if they could make them even stronger and have the Pokemon survive the process. The reason for this is that if the experiment was successful, they could sell the modified DNA sequence to trainers so they could make their Pokemon even stronger. However, the experimental gene was totally adsorbed by the Sawsbuck/Noivern, mutating them and accidentally creating Xerneas and Yveltal ("Xerneas" and "Yveltal" were the names of the experiment, so the resulting Pokemon inherited the names). Yveltal's new power caused it to go crazy and wanting to destroy everything (hence the "destruction" species name), similar to how Noiverns act, only a lot more intense. However, Xerneas was injured by the new super-gene, and had to be slightly robotized in order for it to survive(but not enough for it to receive a secondary Steel typing) (it is the "Life" Pokemon as science has given its life back). It also went crazy from the gene and augmentation, so it escaped from the lab and went back to the forest that was once it's home, but the gene would slightly radiate from it, causing the plants around it to grow, making people think that it was intentionally making the plants grow.