You're pre-supposing that the "present" is the at the end of the timeline, or that this timeline is the only one there is. Or, if you think that it is, then you could still travel to the future by travelling to the past first.
One of the strongest arguments for the lack of possibility of time travel is where are all the time travellers from the future? Why do we still talk about Hitler? Surely, a Holocaust survivor would have travelled back in time by now and killed Hitler as he walked home from school.