It can be a communal experience, everyone sitting around the room enjoying a bar of chocolate, or on a cold winter, everyone sitting around the fire to enjoy a mug of hot cocoa. Thus it is no wonder why sometimes chocolate as well as the other variety, dark chocolate, often appears in dreams as well. There is a meaning to it beyond just frequency though.
To dream of dark chocolate means that you are indulging yourself in something. You are going in for an indulgence that you normally don't allow yourself but because of some specific occasion you have chosen to just take the plunge and just go for it. Maybe your favorite thing in the world is playing skee-ball but because there is such a taboo associated with adults playing it you are afraid to go out and do it so you don't ever get to go have fun. If you dream of dark chocolate it means that you feel like you have done something which was worthy of going out and just indulging that need that you have for this activity.
If there is one thing that chocolate is consistently associated with, it is decadence. People look at chocolate and automatically think of someone going overboard and getting too fat off it. In this sense there is also an element of greed and gluttony. There is such a thing as too much of a good thing and chocolate is one of the things that help to prove this best. Dark chocolate does this even more so. To have a dream in which you are eating dark chocolate this could mean that you are too indulgent in life's pleasures without really doing anything good for yourself or making any positive strides.