Biodiesel is NOT "vegetable oil". It is synthesized from vegetable oil and other bio sources by a complex chemical process of esterification. Idiots who burn SVO (straight vegetable oil) or WVO (waste vegetable oil) or any kind of "grease" in their diesels end up with a disgusting gooey mess in their expensive fuel injection system.
Even true biodiesel has its drawbacks. The viscosity isn't the same as the proper diesel fuel the engine was designed for. That matters when you're dealing with the 1000-bar-plus (15,000 psi-plus) fuel pump of a modern common-rail diesel fuel injection system. It gels and stops flowing at a much higher temperature, and the gelling is harder to deal with than normal diesel fuel gelling. The shelf life is shorter. It is harder on the fuel system seals. Completely unlike normal diesel fuel it is hygroscopic. Once it becomes contaminated with water, bacteria grow and rot filters. Most or all modern diesel engine designs are not rated for any more than 2%, maybe 5% at the most, of biodiesel mixed with regular diesel. The old 1980s-and-before designs were fine with 20%, 80%, or even 100% biodiesel, but those days are gone.