We have to spend billions to upgrade the grid, to handle "Green" power sources that are more expensive than their competitors
Perhaps you haven't noticed, but the U.S. power grid has been having all manner of problems as it is: single-point failures that affect whole cities or entire regions, mismatches between supply and demand that allow Enron-style speculators to manipulate markets, deferred maintenance tallying tens or hundreds of billions of dollars, externalities associated with conventional generation sources that aren't properly taken into account (e.g., nuclear and fly ash disposal).
And those are the problems that we have today, with the grid as it presently exists. Even if no further renewables were added to the grid and Tesla closed up shop tomorrow (both of which are miniscule sources and sinks compared to the grid), we would still need to invest hundreds of billions just to keep things from getting worse. If we're going to gradually rebuild the grid, we should be rebuilding it sensibly: for increased robustness, efficiency, and flexibility. Yes, that means that it can also accommodate renewables and electric vehicles, but that's a secondary motivation.