Often the interviewer is looking for fairly short and concise answers to their questions so they can direct the flow and conversations to what they need to hear through further questions. Filling all the available air time either forces them to rudely interrupt you (which feels awkward) or wait for you to finish even though they aren't that interested in the content.
As an example, if you are asked a very open ended question like "tell me about about role X and company Y.
Start with a brief overview of the role, the company and responsibilities and then pause. Then if they don't immediately ask a more detailed question about the role suggest something. "Would you like to me get into some details about my most recent project/success/challenge?"
Staying brief helps the interviewer get to what they want to know and eases your own burden of maintaining all of the flow in the conversation.