There is a number of contributing factors.
1. Cuban cigars were known as the best cigars in the world pre-revolution.During the revolution a lot of cigar families fled Cuba to produce cigars in countries such as Nicaragua, Honduras, etc. Since then Domestic cigars have continued to evolve and increase in quality. It's safe to say a lot of the best cigars in the world are made outside of Cuba these days. We got it down to a science.
2. Part of the whole mystique behind Cuban cigars in the United States is that they are illegals. I've heard quite some entertaining rumors over the years from non-cigar smokers such as "They put cocaine in Cuban cigars". They are the forbidden fruit which adds to the desire for them.
3. If Cuban cigars were being distributed to the United States, their price point would shoot up dramatically. We would be looking at most Cuban cigars in the $10.00 to $50.00 price range. No way I'm paying that price tag.
Maybe its just me but I'm not all to crazy about Cubans. I think they are great cigars, but not one I had would make my top 10 cigars. Bolivar Petite Corona would be close though.