Why is the wheel bearing grease leaking out of the dust cap?

Well, I agree with that for the most part, I didn't elaborate fully. I spin the rotor forward and backward as I tighten the nut but still back off to the next notch. I have never worn out a set of bearings. I've replaced them that were gunked or worn out before I got the car but I've never installed, drove for years then replaced them due to wear.
People forget sometimes a tapered roller bearing needs some preload.