Fridge Horror: All of the people that Chichikov visits come across mostly as amusing eccentrics. However, he chooses to visit them for a specific reason - they have a lot of "dead souls". As for the reason they have so many to offer? - because of their vices and/or eccentricities, they aren't running their estates competently, and so tons of their serfs are dying - likely through starvation.
The fact that Plyushkin didn't care for his serfs starving is explicitly mentioned. And the fact that some kind of plague happened also helped.
Korobochka and Sobakevich are shown as rather competent squires, but, as it's still soon after an epidemic, many of their serfs are dead, too.