Because the fandom isn't musically based. MLP is a show enjoyable to everyone. And thats the beauty of it y'know? If its a subject of manliness then well, manliness is not based on being strong or tough, but on manners, pride and honesty. Watching MLP, if anything, makes you MORE manly by increasing your horizon of trust, pride and manners. You could be the weakest, shortest least muscled person in the world and you'd still be manly if you kept to your way. I wouldn't get too worried about listening to music that doesn't even relate to the fandom in the slightest way.