The best explanation for why Cuba became a communist government after 1945 is:
due to a lack of economic development and the brutal dictatorship of Fulgencio Batista.
This option accurately reflects the socio-political context in Cuba leading up to the Cuban Revolution in 1959, where widespread discontent with economic inequities and Batista's authoritarian rule contributed to the rise of revolutionary sentiments that ultimately led to the establishment of a communist government.