I'm not saying they should necessarily expect him to be a go-to choice for Borg detail, but if someone in his position were actually doing what's in their best interest, as someone wanting to be a captain, the fact that he'd been at J-25, AND now just sat in the big chair during the saving of Earth, he's in a unique position to sell himself as someone to pretty much take one of the most prominent roles in that initiative. It would be easy to become the face of the Borg front, after this, especially since they're already on their 3rd command offer anyhowWhy should Riker be involved in the Borg fight? He's just a frontline officer who for that very reason hasn't had much time to get down deep on the subject. If something can be established about the Borg at this early date, it's that fighting them with starships isn't likely to work too well. Debrief Riker for what he knows, but then send him back to do the good work of gathering more data for the Borg experts.
At that moment, there is nobody in a better position to lead the initiative on how to deal with starship engagements with Borg. It certainly would shut Shelby the hell up, with her smart-assed "Shadow of a great man" comments, if he was henceforth the Borg hero