I'm not an SP myself but I can try coming up with several factors that may contribute to this increase.
1) Keeping up with competition. Clients that are visiting and giving their money to Asian SP's could be giving that to you instead, no reason to let an opportunity pass
2) Rather than change in morals or religion, I think it's a decline of tradition. Don't get me wrong, the holidays are my favorite time of year. But it's a more family centric celebration. Growing up, my family would always open presents together. However nowadays that I'm older, I really don't do anything. To be honest, I just kind of loafed around in my apartment and watched a couple Christmas movies.
3) On the other hand, it could be seen as a pseudo charitable act. If someone's seeing SP's on Christmas, then they probably feel lonely that they don't have anyone to spend the holiday with. Offering companionship (even for a limited time at a high price) is a kind gesture to them.
4) Places like Vancouver are a melting pot for different peoples. Some may not value or even celebrate Christmas, so there's not any reason keeping them from earning some more money.
I'm just spitballing these, not trying to pass any of these are facts or anything. Just thought it was an interesting quesiton.