Doubling 1N p 3N is useful. Sometimes partner doesn't make the right lead, but if you have a solid major it's usually pretty obvious. There is a huge gain to the double. meanwhile 4C natural will almost never occur. The opps usually don't have a major suit fit, so you having long clubs and a hand that actually wants to bid is quite unlikely. However if you have both majors it's much more likely that you want to bid, and much more likely that you have such a hand.