He said that because it was obvious that the USA would impose an embargo on the island and force most of the world to follow it, it was Castro's fault. He said that if Castro had his people's best interest in heart, he would have caved against american pressure.
It's really funny because even a 5 year old could understand the real reason.
It's because resources = power
US = resources
The Americas in general = resources
The Atlantic is literally baby-mode, the Pacific is godmode