That exemption would make the law useless (trivially circumvented through one more layer of subsidiaries and contractors)

The law can count for subsidiaries and contractors too. No number of layers of corporate shell can stop the workers who need to say "You've reached Apple support, how can I assist you?".

Why should small companies be exempt? If you can't afford to pay people a minimum wage, you shouldn't be in business

Generally the principle is that we should do this “Because additional flexibility with how small businesses are run allows them a greater chance to grow to become bigger businesses. “ but other than that… it’s also just the normal thing in many countries that certain regulations only kick in once your business grows to a certain size. I can thing if several USA and Australian laws like this.

Normal doesn't mean its right, seeing as the normal is currently anyone can do it, big or small, as per this thread and OPs suggestion.

Why should low cap business owners be able to exploit foreign laborers just because they’re low cap?