The reason that I have been given is that the transcripts do nothing to show the demeanor/intonation of the witness and other factors surrounding the testimony. Judges don't want juries obsessing over written material; they want all the circumstances surrounding testimony and all the other evidence considered as well.
Another reason is historical; transcripts didn't used to be ready by the time the jury started deliberations. That's not as true today with computerized transcription which tends to be done in the evening following testimony each day. Even computerized transciption needs to be analyzed and corrected by the court reporter, however. As with computer translations from foreign languages, not all the words come out right straight from the computer. The court reporter has to read through and make corrections.
I had lunch with a judge once and asked him all about this, and this is what he told me.
Actually, I think juries ought to get a transcript to take into the jury room.
Neither do readbacks. I've been on a jury and have had testimony read back to us. The court reporter read it in a flat, monotone voice, never duplicating the tone or demeanor of the witness. I'm sure the court reporter didn't emulate Denise Kamal's body language duting readback :-)
Actually, I think juries ought to get a transcript to take into the jury room
I totally agree with you.