Why did the introduction of sound into film initially impede the movement of actors?

Microphones where initially large and directors were unsure on how to integrate them into films without the audience being put off by the presence of a microphone.  

A popular example of this is the film Singing in the Rain when the producers of the movie decided to make their movie with sound and there was this sequence where they couldn't do the scene because the microphone was in between both of the acts to it got in the way and audio was messed up.