Future Trunks could accomplish a ton if he were still in the picture and it’s exciting to consider how the series would be different if he never returned home. Related.

Future Gohan suffers more than Future Trunks ever does, and there is never any light for him at the end of the tunnel. Future Gohan's childhood was much the same as the main Gohan's.

So when aging Trunks into his teens, Toriyama requested that Trunks became a hero. By wanting to become a hero like Great Saiyaman, well – Trunks has firmly differentiate himself from Future Trunks.