Minimum connection fees, legislated enforced grid connect.
It'll still be a thing in cities because you don't have enough area to collect sunlight for tall buildings on the buildings themselves, but that's also where the costs are lowest because the density is highest. If technology makes it so you no longer need a power grid in rural or suburban areas, and the economics are no longer viable there, why should we pay a lot of money to continue to have one there?
Hypothetically, if the capex to install PV is low enough, and the transmission costs are low enough, then you could build a type of decentralized generator where suburban and rural generation feeds urban demand. There's early work being done on "smart grids" which enable this pattern, but I could imagine a future company that markets to a private homeowner, one who already had sufficient generation for their own needs, with the offer of upgrading their private PV in exchange for most of the generation profits.