I live on the edge of a market town. If I head out into the countryside, everybody will stop and talk. But if I head into the town, conversation stops.
I think it's to do with population density. People are so far and few between in the woods and the fields that it's no great imposition to stop and have a conversation. But in the town centre on market day you're elbowing through the crowds and it's just not physically possible to say hello to everyone.