You've forgotten that we have a limited capacity for solar cell production and those solar cells are put to better use replacing coal plants than synthesizing something plants can synthesize.
Biofuel is just very, very expensive. The only reason it is used at all is heavy, heavy subsidies, often connected with corruption. (Cf. Archer-Daniels-Midland.)
And hydrogen or synth fuel aren't expensive? If these alternatives weren't more expensive then the problem would be moot because the industry would be voluntarily using them already.
They have always been more expensive than petroleum, and anyway would be made with power generated from petroleum or coal, or (in the case of hydrogen) from natural gas.
But that was before solar and wind became substantially cheaper than petroleum.