In fact this may be exactly what parts of the US government want. A hostile dysfunctional authoritarian broken state claiming the mantle of "socialism" (dubious, but whatever) is a great example (along with Venezuela) to point to to say "Why Socialism Bad, See?"
With the sanctions lifted one of two things would likely happen: the "communist" regime would disintegrate under competition, leaving something likely still hostile to the US but not particularly "negative exemplar"is -- like what happened in the eastern bloc -- or it would economically "reform" well enough to function/compete in the world market (like Vietnam or China) while still pretending to be "socialist." Neither of those outcomes are likely outcomes that US capital really wants.
Plus at this point the Cuban economy is heavily dominated by trade competitors to the US. Spanish, Italian, French, and (to a lesser extent) Canadian companies dominate there. Its telecoms systems, electrical grid, energy, etc. are not based on US standards or tech. Non-US companies operate in places and on "property" that US capital still considers to be "theirs" from pre-revolutionary days. Imagine the legal clusterfuck when the blockade/sanctions regime falls apart, and normal trade is attempted again...
In any case, the Cuban people and most normal Cuban exiles aren't doing well out of the status quo. But the Communist Party actually kinda prospers out of this arrangement, and it gives a good drum for right wing politicians in Florida to beat on.
I'm sure Kissinger has some blueprint on this topic somewhere written down, and it's propagated through successive administrations with little to no modification.