The assistant to the host or producer will hold up a sign to clap or they have a automatic sign that will tell them to clap.
Because they are ask to ...... I know from experience I went to a talk show and they have a guy standing off to the side trying to work up the audience and encourage them to act like they are enjoying it whether they are or not.
Because they are told to by the floor manager. It is all orchestrated.
talk shows arent real. it's tv.
:They have to in order to make it and the host look funny.
They have cards that tell them when to applaud.....!!