Companies - managers - very often suffer from the sunk cost fallacy.
They're very concerned they won't necessarily do any better with the next person, than the two hours of work per day they're getting. They've invested into integrating, training the existing employee. Managers almost always consider it a high burden to have to go through the process again with a new person. If they find a considerably superior new candidate first, maybe they'll get rid of the existing person or rotate them into a worse position. The difference between the two persons, in terms of output, has to more than make up for the headache.
They're very concerned they won't necessarily do any better with the next person, than the two hours of work per day they're getting. They've invested into integrating, training the existing employee. Managers almost always consider it a high burden to have to go through the process again with a new person. If they find a considerably superior new candidate first, maybe they'll get rid of the existing person or rotate them into a worse position. The difference between the two persons, in terms of output, has to more than make up for the headache.