It’s not - you can switch a small portion of fuel demand n a sustainable manner. The SAF plants are built purely on economics underpinned by tax credits. The larger issue is that one you get past a certain volume number, the marginal feed stock is soybeans (in the US at least) which for a variety of reasons is structurally more expensive than oil - this is never going to be economic and is a taxpayer funded boondoggle, I wish that weren’t the case