Jonathan Blitzer has a really nice overview of the recent plights of thousands of Cubans who have been stuck in Costa Rica for the last few weeks. Cubans have been leaving the island for Ecuador. Ecuador has lax entry requirements for Cubans. Once in South America, they make the trip north to the United States border in search of the American dream.
However, Nicaragua threw up some roadblocks for the migrants which caused a backlog in Costa Rica. Costa Rica and its neighbors then had to find a workaround in order to help the migrants on their way. In the end, the Cubans were flown to San Salvador and then placed on buses to the Guatemala-Mexico border. They were then on their own to get to Texas and the States. Once at the border, they would apply for asylum, just as 44,000 of their countrymen did last year.
Central American governments have not been happy about facilitating the passage of Cubans fleeing economic difficulties on the island so that they can find jobs and family reunification in the US. At the same time, thousands of people from El Salvador, Guatemala, and Honduras are denied asylum and then returned to very dangerous situations in their home countries. Cubans should not receive privileged treatment over those who are actually fleeing for their lives.
US-Cuban relations are changing. As a result, most people believe that the "wet foot, dry foot" policy that gives Cubans privileges should they make it to the US will end. That is why Cubans are leaving the island now, before US policy changes take effect. We don't know when the policy will change, but they want to make sure that they get in now before it's too late. In that way, the exodus is similar to those Central Americans who left their country in 2014 hoping to take advantage of US immigration law that would allow them to stay. The belief was erroneous, but there was a pull factor as well.
Two other angles that Blitzer could have pursued were the friction caused by "wet foot, dry foot" with Haiti and the immigration backlog that occurred in Guantanamo and Panama. When Cubans were fleeing the island in the 1990s, most believed that the plight of Haitians was worse. Political, security and economic conditions on Haiti were as bad, if not worse, as those of Cuba. However, they were sent back to the island while Cubans were welcomed with open arms. There were protests, including some well know hunger strikes, in the United States. It was an embarrassing and awful episode in the early post Cold War period.
The second angle was the large number of Cuban refugees who were held by US authorities at Guantanamo Bay Naval Base and in Panama. Over 30,000 were held at Guantanamo until the US worked out an agreement with Cuba and other countries about how to proceed. Some of those migrants were moved to US facilities, what looked like prison camps, in Panama as well.
While there are crises causing Central Americans and Cubans to leave their homes and make the perilous journey across the Florida Straits and Mexico, there is no large-scale migration crisis on the US' southern border.