Because of the US trade embargo in 1960. Cuba has had no choice all these years but to keep the vehicles running that they current have. Which means a lot of 1950's cars. This guy took a trip to Havana and took lots of pics on his trip. Most are GM 4 doors. Many repowered with chinese and russian tractor parts according to the article. Intresting read and lots of photos.
A comment was made to me about the evil US that denys Cuba all sorts of goods. One of the things they pointed at was all the old cars as well, hmmm you mean to tell me only America sells cars? The Govt owns everything so nobody makes any money to buy new cars. A Coworker is from Cuba and some of what he says is unreal what they go through. If you are not moving through the black market, your not getting it. He said the place is heaven with the weather and everything the climate has to offer.