Could be a number of things. Parking lots that are large enough would be for commercial buildings (i.e., office building or shopping centers). The owner of the

Could be a number of things. Parking lots that are large enough would be for commercial buildings (i.e., office building or shopping centers). The owner of the building + parking lot might not want to be in the energy production business. And working out a legal agreement with the local power company might be too complicated. For example, a car hits a support for the solar panels. Or a solar panel falls and totals are car. If a panel on a farm falls and kills a cow the downside is relatively minor. The technology is moving fast. The law and lawyers typically don't move as fast.