Originally Posted by kluang
Law have a freaking submarine. He can go through the calm belt
It's exactly like Dagoro said. The calm belt isn't that easy to cross. Just think about how chaotic is was when the SH's accidentally ventured into it at the very beginning of the Grandline. Now think about just how much more crazy the Sea Kings that live in the NW section of it would be.
Another point to consider. We know the Marines coat their ships in seastone so they can cross the calm belt. So in theory they should be able to cross it from either the North or West Blues and go straight there. Yet this apparently isn't the case. Meaning the calm belt and/or weather is so insane they can't make the trip, or they can and raftel itself is inaccessible.