I noticed that there is something there about vocal compared to visual. Some years ago while messing around memorizing/reciting pi, I always thought I imagined the numbers visually and recited from there. I'm bilingual and a friend asked if I can do it in my mother tongue. It was weird, I was surprised I was struggling. I definitely recite(in my head) in English, then I visualize the numbers than I translate.

It was surprising because when I was even younger I thought I had a photographic memory, I noticed it got weak over time and with memorizing some of pi I thought I was bringing it back. And here I find it was mainly vocal. With the points brought up here for oral tradition, it makes sense that vocal memory has stayed strong.