The religion likes to lay out how a person should live their life and they go WAAY overboard with their intrusiveness into people's lives in every area. They might see the idea of people's personal decisions as "vanity" and something they have no control over (which they have no business concerning themselves about - but they do)... It may start dangerous habits, such as Witnesses thinking. And they can't have people in the religion doing that now can they?
I think it is about making JWs different, not for any real reason but just so they'll stand out. No matter what the Holiday is when asked about their plans JWs will end up talking about their religion. What they are after is more attention for the religion.