Unless the Nexus is a nexus point of all times, places, and universes? So that when you jump around, you are actually getting a view into your life in an alternate universe. Now the fact Picard & Kirk exit the Nexus makes less sense to me.
Now I'm just confused, and the fact that Moore and Braga can't come up with a logical explanation either, is unhelpful. Did they take roofies before they wrote, blacked out, and now have no memory of what they were thinking?
The Nexus is not logical, it just is
Star Trek has never been written by physicists, nor should it be. EVER.
I really believe that a lot of people try to overthink this stuff. Just sit back and enjoy it.