Nope, just no economical feedstock supply in sufficient quantity.
Everybody goes crazy over using french fry oil for diesel, but how
much used FF oil is there, anyway? Not enough to make even the
slightest dent in the diesel usage in the USA. Other sources simply
aren't economical now. Economics may play out in the long run, but for
now, it just ain't gonna work, unless of course the gummit mandates it
and (as usual) screws with the laws of economics. It's still a fad for
now.