In the Soviet Union, fields were vast, numerous, and under government supervision. The tractors drivers learned they could get away with ploughing the outsides properly and doing a worse but fast job as they worked inwards. This practice sufficiently tricked the inspectors.
If owned by the drivers, the profit incentives would have motivated them to plough the entire field. The more produce harvested, the more money. If the land proved entirely too big to be managed, the owners would have either hired more people to help or sold a portion of it.