South Korea has a population density of 507/km² [1]

For comparison, the San Francisco Bay Area has a population density of 430/km² [2]

I doubt they have vast tracts of undeveloped land. And while solar panels can replace agricultural land or wooded areas, doing so isn't always a big political win.

[1] https://en.wikipedia.org/wiki/South_Korea [2] https://en.wikipedia.org/wiki/San_Francisco_Bay_Area

South Korea has tons of undeveloped land. Just look at an aerial imagery map. It’s just that it’s quite mountainous and heavily forested. (Not that I think we should tear down the forests for this - surface parking lots are already an inefficient use of space)