Whether you are new to dancing or have attended many social dances, because the music is always playing – and, hopefully, you are always dancing! – there is little opportunity for dancers to actually get to know one another.
On a personal note, not even counting the names that I have forgotten (many of which I forgot immediately), I never even knew the names (or anything about them) of the majority of my fellow dancers.
Dinner dances provide this opportunity to mingle and to chat with others. This happens when you are standing in a line to get food, sitting at a table and/or between showcases, awards, speeches, etc.