A lot of Americans haven't owned American cars since the 70s.
Other Caribbean islands import vehicles that are neither American nor even available in the US.
I know nothing about the auto industry, but South America is not that far away, and apart from tariffs, isn't it demonstrably economically viable to ship things long distances over the ocean? Because people do it, that's where all the consumerism comes from.
And Cuba does have some new cars. People focus on the old cars because it's so visually striking (and those cars are so beautiful!) but it's more a marker of poverty than America somehow threatening to torpedo any ship that brings new cars to Cuba, or convincing all the global auto manufacturers to never sell any cars to Cuba. There are modern BMWs, Toyotas, etc in Cuba right now. Just not many of them. Expectedly, BMW is doing brisk business selling much cheaper motorcycles and scooters in Cuba, which is also true of other Latin American nations.
It doesn't directly. It just makes it harder for Cuba to obtain hard currency to buy new cars.
However, that 'bus' seems to be a locally modified truck, probably a Soviet-built ZiL-164. There is definitely an argument to be made that the cars and trucks produced under Communism, both in the USSR itself and in client states like East Germany, Czechoslovakia and Poland, weren't as good as their contemporary Western equivalents for all sorts of reasons.