I think it's because during the weekdays, the people who have school or jobs resort to more passive activities in their free time such as checking DQN, or another board, listening to music, or mindlessly browsing the internet. On the weekends they have time to set aside a good amount of time for their hobbies, such as marathoning some shows they meant to watch, trying to beat a level in a game, or going to that trendy new restaurant they meant to check out.
That is pretty much what my life is like when I'm not on a break.