That is not true. The US does not block Cuba from getting to the internet in general (https://ofac.treasury.gov/media/912206/download?inline), although it blocks most commerce in general under its embargo. Your linked webpage is a Github policy restricting the availability of Github Enterprise Server and Github Copilot in Cuba, not the internet.
Your characterization of the Mariel boatlift is misleading and wrong. Cubans were mostly not allowed by their government to leave Cuba. During the 1980 Mariel boatlift, Castro suddenly temporarily abolished this policy due to preceding events where thousands had rushed into the Peru embassy in Havana hoping to leave. He announced that foreign relatives of any Cubans who wished to leave could come pick them up in boats in the Mariel harbor. Those wishing to leave where subject to abusive acts of denunciation and beatings by mobs organized by the government. In a cruel twist, Castro then demanded that in addition to their relatives, the boats had to be filled with common prisoners from jails and mental patients, who were given the choice of staying in prison or trying their luck emigrating on those boats. Castro wanted to provoke a crime wave in the US to tarnish the reputations of those Cubans living there. (source: I was one of those Cuban Marielitos that arrived in 1980 in one of those boats).
> Castro then demanded that in addition to their relatives, the boats had to be filled with common prisoners from jails and mental patients, who were given the choice of staying in prison or trying their luck emigrating on those boats. Castro wanted to provoke a crime wave in the US to tarnish the reputations of those Cubans living there.
I can't help but to see a parallel with the out of control flood of migrants (some of them potential legitimate refugees) Turkey let into Europe in order to put pressure on the European Union back in 2015.
Your characterization of the Mariel boatlift is misleading and wrong. Cubans were mostly not allowed by their government to leave Cuba. During the 1980 Mariel boatlift, Castro suddenly temporarily abolished this policy due to preceding events where thousands had rushed into the Peru embassy in Havana hoping to leave. He announced that foreign relatives of any Cubans who wished to leave could come pick them up in boats in the Mariel harbor. Those wishing to leave where subject to abusive acts of denunciation and beatings by mobs organized by the government. In a cruel twist, Castro then demanded that in addition to their relatives, the boats had to be filled with common prisoners from jails and mental patients, who were given the choice of staying in prison or trying their luck emigrating on those boats. Castro wanted to provoke a crime wave in the US to tarnish the reputations of those Cubans living there. (source: I was one of those Cuban Marielitos that arrived in 1980 in one of those boats).