They weren't part of his sentencing because a different court entirely was pursuing the hit for hire attempt charge, but because another court in NY got the book thrown at him for running the site, they decided to drop it because it didn't seem necessary anymore.
In hindsight, the prosecution probably wished they didn't do that, since they are said to have had overwhelming evidence and proof, and there is even a Wired article about chat logs pertaining to DPR seeking services, but those are the breaks! If you don't do your due diligence, criminals can be let off on a technicality too!
I haven't looked into the case(s) for years, but prosecutors don't often just drop charges because other charges were found guilty. People get charged even after life sentences have been handed down.
And you don’t think the prosecutors consider the interests of the FBI when deciding what to prosecute? In cases where they want to use FBI evidence and probably want ongoing cooperation of the FBI for future cases?
In hindsight, the prosecution probably wished they didn't do that, since they are said to have had overwhelming evidence and proof, and there is even a Wired article about chat logs pertaining to DPR seeking services, but those are the breaks! If you don't do your due diligence, criminals can be let off on a technicality too!