At some level, it’s because each platform costs a lot of money. If a game is not available for your platform, it’s super expensive to get another platform. So other platforms having fun games your platform doesn’t can mean losing out— either you won’t get to experience the game, or you’re going to have to shell out, and either way hurts. Thus, it is actively in your best interest if the other platforms fail, thus encouraging devs to spend more effort on your chosen platform.