And how would they do that? The available methods - tax penalties mainly - are too easy to dodge.
Epic handwave. And you're wrong btw. If anything small business outsources even more than large companies. Tons of small business owners have zero US employees but have a personal assistant/CX agent in the Philippines, IT contractor in Latam, design contractors in Eastern Europe, etc.
You would need China-level capital controls to make this work and that is not compatible with the dollar remaining as a reserve currency. Nor will Congress or the Supreme Court go for it.