I suppose part of the explanation is that in Aniara, the ship is always in space but still as far as carrying supplies for years that seems inefficient.
It doesn't have supplies for years, it has supplies for a few months which the crew then eke out by supplementing with edible algae. Since the journey was intended to be three weeks, presumably with a three week turnaround, this seems to be the correct amount of supplies.
Captain: How soon can we increase algae production to cover our food needs?
Officer: Immediately. It won't burden the oxygen system.
Captain: Restaurants? How long can we last? When do we run out of supplies?
Officer: It depends, but in two months we'll start noticing a difference.
Captain: Including the algae?
Officer: We can survive on it.
Everything else the ship needs for its long-term survival is already aboard. It makes its own air, has a water purification plant, carries a handy supply of spare parts and is able to power itself through a nuclear engine.