My pure speculation is they dont want construction access majorly impeded and/or operational/safety issues with constant crossing. I think we at least need to see the area west of the tracks, but probably the entire outside, buttoned up before they lay track outside the tunnel.
can it be done - yes, but theres probably a whole slew of new challenges it brings that are not “necessary”. So the best I hope for is mostly completed track and just needing to fill the gaps and test when it’s time to do so, but I think it’s more than a few weeks.
Hopefully I’m wrong and around the clock crews have the train going in a month!