Depending on your location there may be legal restrictions preventing from US companies hiring you - even through a B2B contract.
But ultimately it depends on the motivation of the company itself, and they use all sorts of excuses to not work with non-US staff
The ones that care to hiring within vetted countries for $reasons usually will not accept exceptions. Notable example is GitHub which has a list of countries they hire from (even though they're owned by MSFT and could hire on the Moon if they wanted).
Having a company is mostly for tax purposes. It makes everything easier. I think the hiring company doesn't care if the contract is done with a business or an individual. Both are usually limited liability and offer no advantage in case of contract breaches.