You really just have to look at where their costs go.
Most of the cost goes into advertising, more than 2 times what goes into research.
They get ads in all forms of media, and the rest goes into the pharmaceutical sales reps. To be spent on their clients. Like bribing, but legal.
This vaccine has been available to Canadians and Europeans for some time now. This is not some new drug, and has been worked on for many years.
I would say, that with a longer average life expectancy than the U.S. and a lower infant mortality rate than either Canada or the U.S., you would be wrong about Cuba not having exceptional healthcare, which is also free to Cubans. The ones fleeing are not fleeing due to healthcare issues.
But keep trying. Maybe you will think of something halfway credible.