Sometimes the job of these people is actually to barge in, interrupt and strike up a conversation, eg: sales. For them, having smalltalk (building a relation with a customer) is being productive.

Barge in to a client meeting when they're trying to close a deal to talk about the latest Marvel movie. I'm confident the sales person will get frustrated with your actions real fast.

These people need to learn that there is a time and place for everything.