It’s a weird rule to have when not explained. Seems like a weird thing to have as a bannable offence, but here is one possible explanation: Jeans are made from thick cotton. Cotton is slow to dry compared to polyester. Cotton when wet is also a very bad insulator, when compared to wool. Wet clothing can also increase chafing. So when hiking and you get wet from rain, streams or sweat, there are other clothing options that are better suited, and in cold climates, it could even be a safety issue.

Agree! They’ve foreshadowed her return so much

That sounds like a slippery slope

I think this is the closest we have ever gotten to being able to answer the question. But yes, it might not ever be completely solvable