Aluminum is metal too.
The Thompson weighs (significantly) more than even an M16, let alone the M4 that actually makes the whole subgun class obsolete. Weighs more, about a fifth the usable range, significantly less terminal effectiveness, not a whole lot going to bat for the Thompson aside from nostalgia.
The 1911 is a great old platform, but let's be real, for people who are in fights determined often by who throws the most projectiles, grenades, bombs, mortar shells, rockets, and artillery, and who have to carry seventy to a hundred pounds of gear with them, going with the heaviest pistol ammunition around in maxed-out weight pistols is not a great idea. Especially since they give up a significant amount of capacity in the process.
The pistol doesn't matter much, but the math going into a troop's load doesn't say much in favor of an all-steel 1911, and honestly doesn't really give much of a reason to issue pistols at all.