puzzling situation
One can only assume they don't want to give the Bundys undue attention by engaging (prosecuting) at the "federal level", which may provide an opportunity to further their
anti-government agenda. By that logic the big mistake was BLM going after the cattle in the first place without the ability to finish the job.
looks like they're leaving the current situation in the hands of the locals yokels. Even if they bungle it, it seems like the right strategy. Just let the thing self-destruct without offering any new PR material.