I agree although I'm not sure if I agree with Jacobi that the main reason is the loss of the repertory system. It has a lot to do with prejudice against what most people of the 20th century thought of as melodramatic 19th century acting. That prejudice seems even more entrenched now with the idea that actors performing with microphones attached to them are more "natural" than actors who use their voices to reach the back rows of the house. The melodramatic sound emerging from the orchestra pit that prompted emotions in the 19th century has now been replaced by an amplified sound design prompting emotions emerging from the sound mixer.
I definitely agree that the loss of the human voice's quality in theater acting is a loss of one of the great pleasures of theater going.