People aren't there to transport
Perhaps this space line has an agreement that it won't leave until all the customers have arrived. Given the time between each flight, this might be reasonable though potentially costly in terms of extra fuel required to compensate for a sub-optimal launch time.
Technical problems
The spaceship toilets are out of order. No one wants to get hit with hyper-velocity feces.
Fueling problems
If a problem with the fuel is found, that will delay departure. Say, the hydrogen is contaminated with something that will really mess up the engines. Purging the tanks, cleaning them and refueling can take a long time.
Space Traffic Control Congestion
There's lots of ships coming and going. As with terrestrial airports, if a take-off window is missed, it may be hours before there's another opening in the take-off schedule.
Worker Strikes
The technicians required to make the station work are on strike. This could be the fuel union, the engine repair union, or the hospitality union.
Piracy
There are pirates in the area and they need to pass before the flight will leave the station.
Kessler Syndrome
Something very big has exploded into lots of pieces that are now spreading out over an important orbit. Finding a hole in all the debris may take some time. Cleaning up a Kessler event will take a very long time.
Solar Weather
Perhaps there's a particularly nasty coronal mass ejection or solar flare headed towards the space port. Given that most trips will happen outside Earth's shielding, intentionally putting humans in the way of such energetic events is willfully negligent. I predict huge court awards against a company who ignores solar weather predictions.