Everyone else can trade with Cuba if they want, we aren’t stopping them.

Eh not quite. It disallows any business following US law or ships trading with the US from doing so with Cuba.

Naturally, there aren't many ships that are gonna trade with Cuba, but not with the 2nd largest economy on the planet right beside it.

Currently Cuba is most lacking in building infrastructure like cement, and medical supplies iirc (even though its medical system and education are world-class), both of which they need to import but can't.