And the optimistic side of me says, these two are not little fish. Chesebro in particular was very involved in planning and architecting the whole thing from what I read. I reckon they must have him nailed to the wall and he knew it from the start, hence the early trial. Probably he has been working on this plea deal from the start but that's a complete guess.
For him to get such an extremely light punishment you'd hope he has something really good to help nail the big fish--there's only one bigger than Chesebro (I don't count loony Rudy). If so, if I was him I'd be hiring some protection because the Trump cultists will be after him.