How does it make more sense? The Lich King was able to use his powers to control the already undead and create more undead. When the Lich King dies, that giant army of undead things would roam and cause havoc. The idea is there must always be a Lich King because that army is quite unstoppable.I think that the creation of the Lich King itself probably created a hole between the Shadowlands and the physical realm. That's why he was so absurdly powerful in the first place.
It's a light retcon, but it sure makes a hell of a lot more sense than the original implication.
But now he was a nexus for the Shadowlands? The fuck? Ha. Blizzard is creatively bankrupt.