Trying to keep my reasoning succinct in order to avoid writing a wall of text:
The soviets were geographically blocked from this being an option
Similarly for Vietnam for different reasons
Cuba doesn’t have the option of dedicating the requisite amount resources(and has the misfortune of being an island next to the most powerful current naval power)
China has the geography to become a great naval power. Sure, it doesn’t have both coasts. It has land connections that led to the Silk Road being a thing on the other, possibly a greater advantage.
They are building up militarily, and seem to be advancing commercial maritime pursuits on this well.
Thoughts?
The Soviet Union took naval power seriously. It just had 4 major areas to defend which meant it was stretched thin.
Elsewhere you mention power projection. The SU wanted to project power to the Baltic, the Black Sea, The Far east, and the Arctic in more or less that order. In all cases distances are small and land basing aircraft generally better. Any projection to Cuba or other allies could be done via subs or a pocket flotilla.
Similarly, China wants to protect power in the South China sea and achieve sea dominance. That's longer ranges and a bigger ask, but China only has to do that and maintain self defence, so the costs are lower overall.
The NATO concept of US Carrier groups or Aus/UK style "We can land the equivalent of two upgunned Marine Expediditionary forces anywhere in the world in a month" is not generally what you want as a nation without hegemony.
Supporting: