The utilities still have to provide the infrastructure
The reason utilities don't pay retail is that your retail rate includes all the infrastructure needed to deliver electricity to your home. And it's still needed in reverse when you want to deliver electricity from your solar panels to the grid. A big part of that is having power plants sitting idle during the day when everybody is delivering solar to the grid so the utility can provide power at night or when it's cloudy. And not every sunny day is in the middle of summer when every kilowatt is needed, but power utilities still have to shut down their plants and take everybody's solar. As an example, consider the huge arguments that have occurred the past couple of years in the Northwest each spring when the rivers are running full. There's actually too much power available, and the hydro people and the wind people are at each other throats over who gets to supply power -- and as a result, who gets paid.
Retail rates for home solar just amount to another subsidy, this time paid by the other customers of the utility. It's just another form of wealth transfer. We may decide that this is socially desirable, but it's certainly NOT justified by the economics.
