How in the world is it invisible?
To be fair, it's not that it's invisible, but more that it's different than how the Japan side is done. As Loka pointed out, the devs did not give the Allies a full production system on purpose, not by accident, so their ships are always "in production" from the code's POV, and thus destroyable. Those calling for a system whereby the long-range production be moved elsewhere, or restored to Portland itself, are asking for a huge can of theoretical worms. Moved where? Arguments ensue. Moved how many? Arguments ensue. If restored at Portland, by when? Arguments ensue. Not to mention a large new code base to be written, not only for Portland, but for every Allied base with ship production.
Ditto those who want rivers to be bridge-droppable or hulk-sinkable. Fine. Code that. There are navigable rivers in the pwhex, and non-navigable. Navigable, such as Rangoon, have tonnage limits imposed. Argue at their quantity if you like, but they're there. If you make it possible for me to sink a hulk in the Colombia River to protect Portland, you also make it possible for Japan to sink a hulk (sourced from where? Any limits on size there? Code that.) in the Irrawaddy so I can't land at Rangoon. And as an Allied veteran of half-a-dozen GCs, I would prefer 50x to be able to land at Rangoon than to have Japan not be able to land at Portland. And if you add bridges, I sure want the ability to CAS their butts out of existence, to stop supplies from flowing across rivers. Totally historic. Everybody good with that? Couple of thousand lines of code, but who cares?
It's a GAME of abstractions. I was playing a mind game yesterday while driving: what are the 20 biggest abstractions in AE? Not having bridges wasn't even in the top-20. People are bitching about a fully-preventable invasion of Portland, but have no problem with seven shiny, new Wildcats teleporting across 4000 miles of open ocean, arriving on an island ready to fly the next day, all because there were 20,000 points of corn flakes under a nearby tarp. Please.
And finally, putting on my schoolmarm suit, the game is finished. Done. Complete. It works like it works. Like it, don't like it, it doesn't matter. It's not going to change. So you either accept that and adapt, or you don't. Canoerebel did the best summary of the options open to the OP. That's just the way it is.
I've been playing this game system since 2005. A month ago I learned that I have been setting LRCAP incorrectly for 13 years. So it goes.