This is propaganda. It is intended to make you think worse of ground mounted solar, the carpark side is to make the message palatable, but isn't comparable. But solar farms in fields is the cheapest way of deploying massive solar plants

Carpark solar is limited to the power infrastructure at the carpark, the limit for commerical building solar in my town is 30kW, the solar farm nearest me (on a sheep field) is 13MW

Commercial buildings get to choose: solar on the roof or solar over the cars. Putting it over the cars will more than double the cost.

So this is, or acts as, propoganda, saying "this effective thing is bad, instead we should do this impossible thing"