Because he si a man, he thinks that he is entitled to decide upon which of the women ought to receive the award. This is a clear piece of evidence supporting androcentrism, but also patriarchy. Through his gesture the man does nothing but put himself at the centre of everyone's attention. Symbolically, his is a declaration that the male is the central value of society hence having the authority to declare and to impose what he considers to have most value. It is true that the award remained in Taylor's possession, but Kanye's gesture was such a blow that her morals were completely down and she was not able to continue her speech, feeling humiliated. In fact afterwards, Beyonce who receives another award will call her out on the stage to have her moment. In the scene under discussion...

This is a clear piece of evidence in support of patriarchy. It is obvious that the man does not care about the authorities which have decided that the award was deserved by Taylor Swift. He knows that his gesture lacks respect and that it is most likely to ruin the winner's moment on stage, but trusting his own male authority he ignores the impact that his action might have.