[Tuna-Fish]

And more to the point, if you want to use synthetic fuels, why on earth would you pick hydrogen?

Yes, it burns to clean water, but if the carbon feedstock is renewable, synthetic hydrocarbons are renewable too. The efficiency loss from doing the additional steps to build hydrocarbons is not large compared to the efficiency losses of using hydrogen, and storage can be so much easier with something denser.

[BadBadJellyBean]

I'd assume because it is complicated. Capturing enough carbon, splitting it, generating enough H2, combining it with the carbon to make long enough chains. That all sounds complicated and expensive and probably needs even more surplus green power that we don't have. It also doesn't solve the problem of local pollution when burning carbon based fuels.

[ACCount37]

Why go for long synthetic chains?

Methane has good energy density, doesn't demand cryogenics or diffuse through steel, burns very cleanly, and can be used in modified gasoline ICEs - without even sacrificing the gasoline fuel capability.