Because they don't like him.

Trumps foreign policy:
>Step 1. Alienate your closest trading partners
>Step 2. Alienate your strategic military allies
>Step 3. Push those alienated allies into the hands of China
>Step 4. Retract all aid to Africa giving up your soft power
>Step 5. Push Africa into the welcoming hands of China
>Step 6. Try to suck Putins cock for over a year
>Step 7. Actually see that Putin is bff with Xi and doesn't care about you
>Step 8. Whine
>Step 9. WINNING! SO MUCH WINNING!!!!

Who cares if you have the biggest army in the world. America is all alone now. Nobody likes you.