A bit of both but the root is that land is comparatively cheap. Building out is economically incentivized over building up. Municipalities can put their thumb on the scale by raising land taxes based on acreage but zoning restrictions are the actual solution (and these tend to be unpopular because the immediate effect is that development costs rise and bring rents with them)
Are there lots of parking lots because it’s sprawling or is it sprawling because there are a lot of parking lots?
A bit of both but the root is that land is comparatively cheap. Building out is economically incentivized over building up. Municipalities can put their thumb on the scale by raising land taxes based on acreage but zoning restrictions are the actual solution (and these tend to be unpopular because the immediate effect is that development costs rise and bring rents with them)