It was all part of the ruse they had for the operation, of Picard being transferred away. But, in the end Starfleet wanted Jelico on the Enterprise in that sector because of HIS experience with the Cardassians and wanted Picard on the mission because of HIS experience with the type of weapon they thought the Cardassians were developing, it wasn't a "snub Riker" thing.
Any other time Picard is thought to be lost it's generally treated as if the Enterprise would carry on with Riker as captain; as Picard says in "Q Who" and what happens when Picard is presumed dead in "Gambit" the Enterprise is allowed detached duty with Riker as captain to investigate what happened. They don't tell Riker to sit tight while we send out a big-boy to take care of things. Hell, it's generally taken that Riker is the captain and will continue to be so when Picard is declared lost in BoBW.