Emulating your conversation partner's actions is a common human behavior classified as "mirroring" and has been known and studied by psychologists for years.
We all tend to subconsciously copy gestures of people we like.
But why do we act like this?
As a rule, mirroring means that conversationalists enjoy their communication and that there's a certain level of agreement between them.
The topic of discussion is equally interesting for both and they know their interests meet.
Repeating someone's behavior is typical of talented communicators, not always because the person is sympathetic, but because there is a goal to be achieved.
This way new idols have been brought to the stage: politicians, celebrities, and other big names.
Popular culture makes people want to look popular, and act and speak like popular people.
Nowadays celebrities steal lyrics from each other and struggle with copyright violation accusations or straightforwardly claim themselves to be the authors, even though all the work was done by other people.
Among celebrities, it's trendy nowadays to use their own speech writers as politicians do.