Why did President Roosevelt cut off all trade with all countries except Britain?

On July 24, Tokyo decided to strengthen its position in terms of its invasion of China by moving through Southeast Asia. Given that France had long occupied parts of the region, and Germany, a Japanese ally, now controlled most of France through Petain's puppet government, France "agreed" to the occupation of its Indo-China colonies. Japan followed up by occupying Cam Ranh naval base, 800 miles from the Philippines, where Americans had troops, and the British base at Singapore.