It wasn't long after the year of four emporers, and something like a major volcanic eruption would threaten the food supply and infrastructure of even a modern power. Was there something special about Rome that enabled it to withstand this environmental disaster relatively unscathed?
According to Pliny the Younger's account, the eruption only actually destroyed an area accounting for about 10 square miles with ash and mud. Pompeii and Herculaneum, while both Italian cities, were not by any real means a metropolis or cultural or economic center. The deaths of several thousand people, while tragic, just don't stack up to the economics of Rome.
Pompeii, as far as I am aware, was something of a holiday spot and was known for its brothels and rather 'bawdy' activities. There was no doubt a loss to the wealth of the Senatorial class when all that vacation property and luxury was wiped out, but that's personal wealth and not national. And not to be crass, but that's a hit just about any national economy would be fine with taking. Now, if this were a massive port or a central crossroads city, or a farming hub, the story might be quite different.