Mod authors have all the rights to their mods. If Bestheda were to use their work they would have to come to an agreement of a sort with the authors of the mods. Bethesda didn't make the changes to the game, the authors did. Many authors have made astounding improvements to the worth several hours of work time. If Bestheda were to take mod content without an agreement, and claiming it as their own, they would be stealing and facing several court cases not soon after. A mod author has every right their work.
Authors benefit plenty (they get their name out in the industry), they just can't make a profit from it. Since Bethesda can't charge for bringing mods to consoles there isn't much motivation to do so, except for the heartfelt goodwill found in their heart. (Does it even exist?!) Odds are extremely high that it will never happen.