Sci-fi and Time Travel

I was watching Star Trek:TNG and ST:DS9 last night. Both episodes were about time travel.

In Star Trek:TNG, Picard was jumping to the past, present and future. Seeing things that may or may not have happened.

In Star Trek:DS9, Chief O'Brien was jumping forward 5 hours into the future and then returning to the present. In both cases, there were some sort of sub-space anomaly that triggered their jump through time.

I know these shows are science fiction and it's not real. But it got me thinking. Why is it that in these shows, most time travel happens in space or in another planet? Could it be that time travel happens whenever there is a phenomenon out there in the far reaches of space?

From my understanding of physics, time is affected as gravity gets stronger. Such as Einstein's theory that if person A is travelling to the event horizon of a black hole and because of the strong gravitational forces, person A, near the event horizon thinks time is constant, but an observer, person B, far from the event horizon will see that the person near the event horizon takes a long time to reach it to the point that he seems to have stopped.

So when person A returns back to the place where person B is, more time has passed for person B than for person A. So what might have been a 1 day trip for person A, could have been 10 years for person B.

So because the solar system has none of these strong gravitational forces. It got me wondering on whether Earth is unique in supporting life because it has a lot of stable systems? Stable atmosphere, biosphere, weather, gravity, planetary system and stable temporal system.

It would be hard to life to exist if time keeps jumping forward and back. Or if time is too fast or too slow.