How is Winter Bash different from the traditional gamification on Stack Exchange websites? What is the purpose?
It's different because it's temporary and more fun-oriented than the reputation and badge systems.
After all the hard work this year, and the whole situation with the pandemic, we deserve some kind of party or holiday, and Winter Bash is exactly that. It also helps increasing participation and traffic in a period that is otherwise known for low activity; most of the traffic to the network is Stack Overflow and many of those programmers searching for solutions to problems they face at work are on holiday right now.