There's a lot of entirely unsupported statements here that seem to be nothing more than uneducated opinion.

You assume there's still a lot of rooftop space that doesn't already have solar on it. SK has very high population density and long started moving toward "less efficient" installs like balcony solar because most 'easy' rooftops already have solar on them. Remember: the rest of the world is way ahead of the US on this stuff. The UK for example regularly sees nearly 100% renewable powering of their grid plus 'recharging' their pumped hydro and BSS reserves.

You declare that covered parking solar is more expensive than rooftop, with no supporting evidence whatsoever. Rooftop solar involves a great deal of site-specific design work, and a ton of on-site, dangerous labor, and usually has to meet tighter code standards. Rooftop work is some of the most dangerous work one can do; that makes it more expensive labor but also injuries and deaths have a substantial cost to society. And labor has to be more skilled.

Parking lot solar setups can be almost entirely assembled in factories, highly standardized down to just about the ground. That reduces parts, eases supply chains, sales inventory, repairs, etc. Final bolt-together and wiring connections are fast, easy, and don't require skilled labor. "Bolt this stuff together, plug this into this." Used or partially damaged systems and their components can be easily repaired or reused elsewhere.

Parking lot solar encompasses a LOT of panels which is more efficient as fixed costs are spread out more; rooftop solar is generally less-so because it's smaller and as mentioned involves a lot of site-specific work.

You ignore the energy savings from the cars being much cooler and not needing to waste as much energy. Being shaded also means the paint, trim, interior, etc stay in better condition longer.

You ignore that solar on-site coupled with EV chargers on site eliminates a lot of grid transmission losses. In theory a residential complex, employer, retail, or commercial site could set up something like this, pumping most of the energy into the cars parked underneath, and have a fairly small connection to the grid.

Bifacial panels suspended well over the ground can collect a not-insignificant amount of energy from their underside.

Solar panels suspended where they have lots of airflow over and under them run cooler, and produce more electricity.

You don't seem very well informed on the subject and probably shouldn't be commenting so confidently.

South Korea Mandates Solar Panels for Public Parking Lots