The dwarfs had always been isolationists, and with the curse killing the human world they had a reason to indulge their most paranoid instincts. The gates of their great halls were sealed, but that was only a temporary solution. Once they had a reasonable semblance of security, they fell restarted all their old feuds. Now, however, the old arguments were framed by a larger concern: how to survive. The surface world would not be reconquered, that was agreed. They must reclaim their most ancient heritage and seek self-sufficiency underground. The dwarven kingdoms almost erupted in civil war over how this could best be done.
Eventually, it was decided that every hall should be allowed to take its own path. A single strategy would either fail or succeed, but out of one hundred strategies, surely at least one would succeed. They constructed great vaults, each with its own strategy for self-sufficiency, survival, and security.
Many vaults have been discovered by adventurers over the years. They are treasure troves of technology, magic, and lore, but the one thing they have in common is a lack of living dwarves. So far, no successful vault has been discovered. What has been discovered includes a vault shielded against all magic that developed sophisticated gearwork and explosive powder, a massive terrarium vault containing the last of the thunder lizards, and a populated vault, populated not by dwarves but by intelligent fungi that seem to have hijacked their bodies. There are surely many others.