Probably just the simple economics of cost of land vs cost of construction of a new building + ongoing maintenance.
I'm sure if they ever saw need to place this in a city they would construct a building. But for now, it's probably cheaper to just build out where land is cheap (and possibly closer to generation source) and then transport the energy to where it's being used.
I'm sure if they ever saw need to place this in a city they would construct a building. But for now, it's probably cheaper to just build out where land is cheap (and possibly closer to generation source) and then transport the energy to where it's being used.