The main reason why we discourage people from talking is that it distracts others who are trying to learn.
A while back, we had a visitor from another dojo. He was in town for a couple of months and wanted to train with us. On the first day, he spent a lot of time talking during class with the other students. I asked him to please refrain from talking. Later on in the class, he raised his hand to ask a question. I told said to him, "Please save your questions until after class." Then I explained that Aikido is a experiential pursuit that needed to be experience on a physical level first. He kept his hand up. I further explained that the techniques cannot be learned with the mind and like, "a picture is worth a thousand words" talking about the techniques would only create further confusion. Subsequently, the student waited for other students outside and complained about the "no talking" policy. He never returned.
I would love to sit and have a conversation about Aikido, philosophy or the techniques. But, the truth is that we don't have the time and what little time we have I would rather spend it having the students put the time and energy into improving their techniques. One of the biggest lessons I learned about teaching is that there is a thin line between teaching and talking. One is for the students and the other is for my ego. Do you find that the same is true for you?
If you must talk, please keep your talking to a minimum and use the slightest hushed tone.