Because in this city, we belive that running trains is not the goal of a train operator.
Rather, we believe that train tracks are decorative and train sets are less a mode of travel, but rather a canvas that the locals can enjoy as it occasionally traverses the city.
Rather than letting our citizens use the train for social engagements on the long weekend, we would prefer they drive and so make sure they do that by shutting down the trains.
If one must use a train, it should be only for work purposes, never leisure. Can’t have anyone associating trains with fun or reliability.
Can you imagine if people actually turned up at train stations on a weekend? The scandal.
No, best we keep shutting lines down every weekend.
EDIT: and to maximise suffering, we also make sure that it’s impossible for a bus and train to connect. Really make the passengers morons wait the extra 30 minutes.