"Well if the traveling to the past is possible why nobody hasn't come yet from the future?"
Maybe our world ended before we could build a functioning time machine.
So, there must be either alternate timelines or parallel universes for "time travel" to be possible.
Think of the grandpa paradoxon. If i travel back in time to kill my granpa, so, there i am, standing in front of him, holding a gun. I shoot and he's dead.
Version 1:
My past stays, but the future is changed. So, if i wanted to go back to my time (the OLD future) i'd have to travel BACK in time!
Version 2:
My past is eliminated and i'm stuck.
BUT time is either a constant, then you can't break out of your timeline.
Or it's not a constant, then you wouldn't be able to travel to a specific "place on the timeline".