BS. There is no good reason why Session’s recused himself. It’s a self recusal so it’s 100% up to him. If Rosenstein can stay on after signing the FISA warrants and Mueller can be appointed with all his conflicts and relationship with Comey, then Sessions should have stayed on. But he’s part of the swamp.
1. If a prosecutor recuses himself in a case when a recusal isn't really necessary, then someone else just does his job in that case.
2. If a prosecutor doesn't recuse himself in a case when a recusal is warranted, then the successful prosecution of the case is jeopardized.
This is why a prosecutor who actually wants to prosecute a case and doesn't want the charges to be thrown out later will usually decide in favor of a recusal if there is a legitimate question about a potential conflict of interest.
Now go back and look at the apparent conflicts with Rosenstein and Mueller in this context. Do you get the impression that they ever expected any criminal charges that came out of Mueller's investigation to stick? After seeing how amateurish Mueller's team has been in the Concord Management case, I'd say: absolutely not.