Well, AMLO and Cárdenas are both openly Fidel Castro fans, and both mourned his death:

https://www.proceso.com.mx/464144/fidel-castro-gigante-a-la-altura-nelson-mandela-amlo

http://www.milenio.com/internacional/el-dia-que-cuauhtemoc-cardenas-conocio-a-fidel

The collapse of Venezuela is ongoing, and what the charge of Chavismo means is different from what Fidelismo might mean. It’s like how many leaders have been compared to Trump. The reason AMLO is compared to Chávez is because he is a charismatic left-ish populist with huge promises that mobilize the poor. Mexico is a young democracy, just like Venezuela was when Chavez won. Chávez won democratically and was a legitimate leader. People loved his personality and spirit, and now Venezuela has gone from being rich and powerful with a democratic system to an impoverished violent dictatorship hundreds of thousands of people are fleeing.

It’s a fear about flawed democracies being overtaken by populists who consolidate power to achieve huge goals and then mismanage the society into chaos, hunger, and dictatorship. It wouldn’t make as much sense to scare people by comparing Cardenas to Castro. Castro was a guerrilla leader who spread insurrection, and importantly stoked fears about the Soviet Union taking over American governments. In the recent Colombian elections, the failed candidate Gustavo Petro was accused of “fidelchavismo” but that situation’s different, Colombia is going through a peace process with a huge pro-Fidel guerrilla army that was a part of an internal conflict that displaced five million people.

They don’t just say Chavez because he’s left wing like people used to say Castro as the current left wing boogeyman. It’s a specific fear of radical populism crashing democracies. The specific fear of Fidelismo in the 80s would be directed at someone like Daniel Ortega who was waging guerrilla war in the Americas.