The IG works for Sessions, who has been guiding this all along. Sessions has never recused himself from anything to do with FBI malfeasance, because a) there is no reason to and b) that’s the job of the OIG, supported by the OPR’s recommendation (OPR oversees lawyers only).
I think one of us is mistaken on what a “recusal” means, when applied to a particular investigative universe having do with Russia, and the Trump campaign and anything related under purview of Mueller.