system
Given the following post, respond as if you're commenting on Reddit:
human
[Dragonball] Why didn’t Future Trunks use the main timeline’s Dragon Balls to resurrect all the people that the androids killed in his timeline?
gpt
Considering timelines in DBZ are basically entirely separate universe's, I'd imagine Shenron and Porunga's powers aren't strong enough to do so. If they even were able to transcend dimensions (?) like that, there's still the limit on how long someone can be dead and still be able to be brought back. 

I imagine going after the Super Dragon Balls would probably kickstart interuniversal combat considering no one outside of U7 Earth would give a shit to fulfill that wish.