Why do Interviewers talk over Interviewees ?

They do it when the interviewee insists on ploughing on with a prepared statement rather than answering the question.

What did Starmer say about Sunaks rude behaviour “if I can get a word in edge ways “ Too many overpaid celebrities posing as journalists.

It happens because politicians have certain things they want to say and other things they don’t want to be asked about, so they will just keep talking to fill up the time available for the interview. Also, they will answer a question by starting down a road to saying what they want to say, rather than answering the question properly. Good interviewers interrupt because their job is to try to get the buggers to answer the damn question 🤷‍♀️

I suspect the interviewer has an agenda they have to keep to and they probably have the producer's voice in their ear saying "Ask this or that and you've got three minutes" or "make him get a move on and wind up." Not as easy a job as it looks. But yes - sometimes they interrupt while the interviewee is saying something really interesting.

I think the various political interviewees have been instructed to keep talking, regardless of the relevance to the question asked.
I thought this was particularly evident in the Badenoch interview. She had a set of stock answers which had little to do with the questions asked - determined to just sound authoritative and keep going regardless.
End result - no-one was any the wiser.

can't stand Naga Munchetty either,,,she always looks as if she's looking down her nose at you

Ditto

In my view it's lack of training.

I dont think it is lack of training as such but more like they are trained to behave like this especially the BBC.