You are so naive to think that US actually cares about democracy. Do you ever wonder why they invaded Iraq two times, but never really bothered to invade Cuba, which is in their backyard? Because Cuba has nothing of value, no natural resources, no valuable technologies. So the US tolerates communist regime in Cuba, because there's no money in invading it.

I will disregard "Bay of Pigs Invasion", since that wasn't really US military operation, but some small scale, CIA orchestrated coup.