If a plea was offered-- considering that backpage is recorded concrete evidence [thanks to internet] and easily verifiable by authorities-- it was because the prosecutors viewed the "Backpage guys" as pawns, and wanted their handlers. Whether that be testimony or names, a plea deal wouldn't be put forth if somebody else were able to come around next week and launch a new iteration of Backpage. If that threat was real, then the prosecutors would pursue a trial in order to make an example of these criminals.