At this point, it has very little to do with communism. Florida is a big primary state and a big electoral state. Florida has a lot of Cuban-americans who would prefer we invade the island. They have traditionally fiercely opposed lifting the sanctions.
Evidently this isn't as true as it was. Still, outside of cuban americans, not many people care one way or the other.
Thus, politicians gain very little and risk quite a bit by opposing the sanctions.
And yes, it is fucking stupid on multiple levels: it was probably always counter-productive, political leaders should show some fucking backbone and end it, citizens shouldn't be so apathetic about keeping an entire nation impoverished, and
why is florida even allowed to vote?
But, dumb as all that is, "we still hate communism" is not a big reason why we still have sanctions.