...Because you can't handle the truth, that's why! (Jack Nicolson mode off)
(Seriously) Biodiesel is an ester, which means it has a lipid (oily) part and an alcohol part. The algae or jatropha supply the lipid, the alcohol is still required.
Ask anyone who has made their own biodiesel - although they use old french-fry oil, they are also mixing it with methanol (if you want to do the reaction at room temp, the ethanol reaction requires heat) and lye.
There is no royal road to geometry. -- Euclid