For me, it's a bunch of things. It happens once a year, so it feels special. Many of my friends (and sometimes coworkers) try it as well, so it turns into something to chat about. Because they're one a day they end up being timeboxed, I can focus on just hammering out a solution or dig in and optimize but I can't move on so when I'm done for the day I'm done. It's also pretty nostalgic for me, I started working on it in high school.