I suppose it might be a question of who would be willing to do it? Philip isn't exactly known for being friendly and open with reporters so I imagine many of them would shy away from trying to get him to talk personally. Titchmarsh of course will do anything. Didn't see it. Really don't care what he has done or how he feels about it all. (and he's not going to tell about the really interesting-scandalous- bits is he?)
I didn't bother to watch, because I think Prince Philip is his own man, and although he has served the country and the Queen well, he will always be a private man, and no interviewer is ever going to get beyond the public man. Waste of time, we can, if we want, look at archives and appreciate the work that he has done, don't need any 'insight'.
A good opportunity was missed here and the wrong interviewer was sent to do the interview. Philip does not suffer fools gladly and was clearly irritated by the questions asked. You don't ask Philip how he felt, he'd just say we didn't feel, we just B well got on with it. How did fatherhood affect you? Etc Many years ago Philip descended from a plane and was met with, "How was your flight sir?" Philip, "Have you ever flown?" "Yes sir, many times." Philip, " Well, it was like that!" Titchmarsh is a lovely man but he should stick to gardening. He's not a journalist. Who do you think would have done a better job interviewing such a fascinating intelligent man as Philip?