As others said, staff, sanitation, and I would add wear and tear on the rides. Continuous operation can't be good for them (and neither can no operation...I hope someone is running them weekly or something). Running a 24 hour event at MK is different than continuous operation. Even in normal times, there was a night crew who cleaned every park every night. That's why sidewalks are wet in the morning. Even during the 24 hour events, rides were still on a schedule with certain ones being closed for a few hours, presumably for safety checks.