Even if rabbits never have any health problems they’ll need to be vaccinated every year and checked out by a rabbit-savvy vet. A member of staff will need to make sure this happens. If they do get ill and medication has to be given over weekends, or a series of vet trips it all takes up valuable time.
Also, sometimes a bond between a pair of rabbits can break down. If this happens, they’ll need supervising for a while to make sure they don’t need permanently separating. This is a big ask for busy staff.