Because it has lots and lots, of good, cool, super fun games in all genres.
And I love playing them.
And in the case of 2d and 3d fighters, it has fun games like Powerstone, Project Justice, Vampire Chronicles aka Dark Stalkers, Marvel vs. Capcom 1 and 2, Super Street Fighter 2 Turbo, Plasma Sword, Fighting Vipers 2. Advanced 3d fighting games like Virtua Fighter 3tb, and we were even lucky to get, the best Soul Calibur game on it too.