Looking at the community, the rule is not enforced. There are other not open-ended questions up and doing fine. At best, assuming this is intended to be enforced, it's being enforced selectively.
Assuming you're being perfectly honest and fair, this rule should be changed. Questions that require elaboration from "yes/no" should be (and are seemingly) allowed. Sure, questions that can only be answered with a "yes/no" aren't providing a discussion. The trolley problem, for example, can be answered with a yes or no, but invites people to expand on why.
I don't have an issue with it. Nudity is natural. It's an American thing to think people need to be sheltered from it.
However, I don't know if Barbie was targeting a young audience. They certainly weren't excluded, but I think at least half of their target were millennials. I'm a man, and I know a lot of my peers, and myself, watched it and enjoyed it. I'm pretty sure the thought was probably a movie for the parents that the kids will also want to watch.
(Also, kids are not watching these events. Even if they love the movie, they aren't going to watch this press event.)