In politics it's helpful to have an antagonist to point at and blame for everything bad. There's a villain in every story, and I best point him out to you in case you think it's me.

Cuba is somewhat unique in that there are lot of ex-Cubans clustered in Florida, a swing state, who are there by virtue of being anti-Cuban-government. They are in favor of any policy that hurts the govt, even if it hurts the people left in Cuba more.

Ultimately all this animosity boils down to the nationalisation of private (US) property in the 60s. An unforgivable crime As Amerixan William Wallace might have said "you can take our freedom, but you can't take our money."

Politically though being anti-Cuban has little downside, and wins important votes.