Also, the only people who should be allowed by Liberty into Zone 21 should be those authorized by High Command, really. Even Navy and LSF officers (like Juni and possibly Walker) are not generally allowed in.
The Zone 21 gate is a particularily special one, given we have explicit campaign evidence of a former high ranking Navy officer transmitting codes to open it. You can argue it was on heightened alert, but I doubt they wouldn't keep something like Alaska kept under a massive code sequence. I mean, they built a massive minefield around it.
As to why the 2 battleship solution hasn't been implemented.. it's because Igiss wants the mod to be SP playable. Which I, with respect to him, don't get, given that you can read about the Nomads and news from 16 years later (including reading about the Kusari Bretonia war when frontline news is speculating about the first interhouse war!) early on in the campaign.