Your sample was Korean to English subtitlers, so they either live in English-speaking countries or their second language after Korean is English. So their responses would be expected to be English-centric, a way of writing that is comfortable to native English speakers.
However, we all know that native English speakers are not the only ones to consume English subtitles. Most European languages would be more comfortable with U romanized as U and not OO, because for us “oo” is just a double “o”.
Actually, I was surprised that in two out of three cases they did stick to RR. (I’m not counting the Song question, that was too obvious, what else would one put?)
It was interesting that they were not consistent in their choice. For instance they chose “oo” instead of u in 숭, but they didn’t choose “u” instead of “eo” in 성
This mixture is very confusing in my opinion. Either use the colonial style of u for eo and oo for u, or use the RR, not picking and choosing bits of one and bits of the other.