Because, we have very limited oversight, influence and control over a foreign corporation. Especially, with one that has links to an adversarial government. Normally, not a big deal for most things outside of national defense. However, SM is the atomic bomb of propaganda - the most powerful weapon ever built. Thinking of it that way, allowing US contractors to build, maintain and sometimes test those weapons on US soil is one thing. Imagine if we were letting China do that (we are), it's inconceivable. Full disclosure, I actually love TT and know that when it gets banned a good enough clone (not named FB Reels) will take its place.