Why dismiss time travel as an explanation?

I ask this in all humility and with respect. I have an open mind and am trying to learn what I can. One idea that has come up in serious discussion (I forget where, unfortunately) is that perhaps an alien race might have technology that would allow them travel from one point in space to another point faster than light, or at least at a speed or in a manner that seems impossible to us given our current understanding of physics. (I don’t like to use sci-fi terms like “FTL” or “worm hole” because I don’t want to be trite.)

Well, if we are open to technologies that go beyond our current understanding of physics, couldn’t we also be open to time travel? A hypothesis that these phenomena are explained by human technologies from the future might even be simpler than the extraterrestrial hypothesis. The time travel hypothesis requires only a single unfathomable technology (time travel); the extraterrestrial hypothesis requires both an alien civilization as well as an unfathomable technology (their “FTL”-like mode of travel).

Is there a reason why a time travel hypothesis has been dismissed? Has it ever been discussed with any level of seriousness? As I said at the beginning, I’m just trying to learn what I can.

Thanks for any help!