Presumably, after the Dominion War, there were all of about three people still alive who were captains before the war. Unfortunately, Sisko became God and Picard was an ex-Borg security risk. So Janeway it was.
I take it that is from Trek lit? Are they assuming that a bunch of Admirals died during the war too?
No. I mean, probably not. Nechayev and Ross are still alive, anyway.