*laughs in littoral combat ship*
Seriously though that IS a good idea, and it’d be kind of neat if ships could carry armed cargo on their dock ports...
But one big focus of the TEI designs was strategic endurance, and while that lends itself to modular and easily repaired weapon/armor mounts, it means you want your ship to be a tightly integrated and very stable piece of machinery. Big detachable mission modules (like those which have failed so badly on the LCS) and a multipurpose frame weren’t as important as having a single, reliable, easily repaired design.