Why? Sunlight falls everywhere. It’s not obvious to me that there should be efficiencies in capturing solar power centrally and then moving the energy over transmission lines.

If you want one rooftop’s worth of electricity, you can either pay someone else for a rooftop’s worth of real estate and have them run solar panels on it, and transmit the power to you over wires, or you can put solar panels on the rooftop-sized area you already own at zero marginal land cost, and have the electricity already right where you want it.

That that works out economically doesn’t seem like a surprise.